The life of a fluorescent lamp is essentially determined by life of the cathode filament it uses. A conventional fluorescent lamp employs closely wound coil of tungsten wire as filament. Upon switching on the lamp, electric current passing through the filament will raise the temperature of the filament that in turn will generate thermions (electrons generated by a thermal process). Thermions are necessary to initiate electric-discharge through the column of the fluorescent lamp.

Frequent switching on/off the fluorescent lamp occurs through several cycles of filament heating and cooling. If the cycles of heating and cooling of the filament are too frequent this may result in tremendous loss of oxide coating (at the rate of 10-20 micro-grams/cm{+2} per cycle).

The loss of oxide coating in the cathode filament through rapid on/off (heating/cooling) operations will lead to poor performance of the filament in generating thermions to initiate the discharge process. This in turn will reduce the life of the fluorescent lamp. Life of a conventional fluorescent lamp usually rated for several thousand hours of continuous burning can be halved or made still less, just by frequent switching on/off. Courtesy : The Hindu

How is a ventriloquist able to throw his voice?

ANSWER I : Ventriloquism is the art of projecting or ‘throwing,’ the voice so that is appears to come from a different source. The performer also directs the attention of the audience to the place from where the sound is supposed to come.

The sounds are produced in the usual method adopted in talking, but the lips are held as nearly and motionless. Sounds are modified by the throat and palate. Consonants are often changed to avoid lip-moving syllables. Lack of facial expression on the part of the performer helps to fool the audience.

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ANSWER II : Ventriloquism relies on the fact that the ability of the human ear to locate the source of a sound without visual and other cues is very poor. What the ventriloquist does is to supply misleading cues through the use of what we ‘masters of deceit’ refer to as stagecraft and voice. Stagecraft consists of using gestures, eye movements, patter, and so on to direct attention to wherever the voice is supposed to be coming from.

Ventriloquism is the ability, not only to talk without moving your lips but also to alter the pitch and cadence of your voice so as to create a second personality, which you can then bestow on the object of your choice.

Scientists have explained the trick of ventriloquist in detail, and have managed to produce the reverse effect — where people are tricked into believing their ears over their eyes.

People place different amounts of faith in their different senses. This is exploited by ventriloquists, who fool us into thinking sound is coming from someplace it isn’t by relying on the fact that people use their vision more heavily than their hearing to locate the source of a sound. This is because the eye’s retina is very sensitive to the direction of light that hits it, while the ear isn’t so sensitive to the direction of a noise.

The cinema is the classic ventriloquist effect. It is assumed the voices are coming from the actors on the screen instead of from the loudspeaker kept somewhere else in the room.

There are only six tough sounds the ‘labials,’ or lip sounds, b, f, m, p, v, and w. Essentially what one does is to substitute some vaguely similar sound, talk fast, and let people hear what they want to hear. For ‘w’, for instance, ‘oo’ is substituted and ‘where’ becomes ‘oo-air’, ‘twenty’ becomes ‘too-en-tee’. — The Hindu S & T Desk Courtesy : The Hindu

What is the peculiar smell of the earth after the first shower?

ANSWER I :The characteristic earthy odour of soil is caused by the production of a series of streptomycete metabolites called geosmins.

These substances are sesquiterpenoid compounds and unsaturated compound of carbon, oxygen and hydrogen. The geosmins first discovered has the chemical name trans-1, 10-dimethyl-trans-9-decalol; however, other volatile products produced by certain species of Streptomyces may also be responsible for the characteristic smell.

An unforgettable attribute of the streptomycetes is the musty odour they emit, an odour reminiscent of freshly turned soil.

Streptomyces are primarily soil micro-organisms requiring a lower potential for growth. The most significant environmental adaptation of the Streptomyces group is their ability to withstand dessication. Geosmins are also produced by some cyanobacteria.

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ANSWER II : The piquant, musky odour that hangs in the air emanates from an odorous chemical buried in the soil called ‘geosmin’ (literally, earth smell).

The smell is given off by Streptomyces bacteria, a genus belonging to the Actinomycetales order of Gram-positive eubacteria, also called actinomycetes. The soil normally contains a multitude of environmental saprophytic fungi.

Actinomycetes, a type of filamentous bacteria grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produces the geosmin spores in the soil. Rain hitting the ground kicks up an aerosol of water and soil and spores into the air, where they are easier to smell. (just like an aerosol air freshener).

We breathe in fine particles of soil containing the bacteria.

ANSWER III : A pleasant smell after the first shower is because of a group of filamentous bacteria Actinomycetes found in the soil. They grow well in soil when the conditions are damp and warm.

When the soil is too hot, the bacteria are not able to tolerate the dessication, so it produces spores as survival strategies. The spores remain invulnerable for years and are resistant to dessication and heat. During the rainfall, the spores are taken up in the air by the force of wind and suspended in the air as aerosol. When we breathe the air, which contains spores, we are able to feel the earthy “after the rain smell”. Geosmine (dimethyl-9-decalols) is the microbial product found in the spores is responsible for the pleasant smell. Courtesy : The Hindu

How does a rechargeable battery work? What is the life of such batteries and how are they different from ordinary batteries?

Electrochemical cells and batteries are identified generally as primary and secondary batteries. The primary batteries cannot be easily or effectively re-charged electrically and hence are discharged (used) and discarded. The electrochemical reactions in primary cells are not easily reversible. When the battery delivers current (during use) the active materials undergo changes and the active materials slowly will become inactive because the discharged active materials can’t deliver current. In secondary batteries (example., lead-acid) the reactions are said to be reversible because once the battery is used, the inactive materials can be converted back to active materials by re-charging and the battery will be again ready for use.

These systems are also called as ‘storage batteries’. (example., lead-acid, nickel-cadmium) In the primary category, for example., zn-carbon cells, the anode is zinc and cathode is manganese dioxide. During discharge (when battery in use), the simplified reaction can be written as (the actual electrochemical process is more complicated)

Zn + 2 MnO{-2} ZnO + Mn{-2}O{-3}

Discharge (delivers current)

The discharged products (right hand side) cannot be formed back into original active materials (left hand side) by passing current in an opposite direction (charging). It is said to be ‘irreversible’

Where as in secondary batteries, for example., lead-acid, the active materials can be formed back after discharge (use) and it will be ready for use again after charge.

Pb + PbO{-2} + 2H{-2}SO{-4}

Technically some primary batteries can be recharged for several cycles but may not deliver full capacity and may have poor charge retention after recharge. Generally the cells are not designed for that type of use. The life of a secondary battery (lead-acid or nickel-cadmium) may vary from 200-1200 cycles (one cycle represents one discharge and charge) depending on its design parameters. Courtesy : The Hindu

Why is fuel used in airplanes different from those used in motor vehicles?

Aviation turbine fuels are used for powering jet and turbo-prop engine aircraft. Kerosene was used to fuel the first turbine engines. Kerosene-type fuel was chosen as having the best combination of properties.

As the primary function of aviation turbine fuel (jet fuel) is to power an aircraft, energy content and combustion quality are key fuel performance properties. Other significant performance properties are stability, lubricity, fluidity, volatility, non-corrosivity, and cleanliness. Besides providing a source of energy, fuel is also used as a hydraulic fluid in engine control systems and as a coolant for certain fuel system components.

However, compared to a kerosene-type fuel, other type fuels like used in motor vehicles were found to have operational disadvantages due to their higher volatility:

Greater losses due to evaporation at high altitudes.

Greater risk of fire during handling on the ground.

Crashes of planes fuelled with wide-cut fuel were less survivable.

Lighter (less dense) fuels, such as gasoline, have higher heating values on a weight basis: whereas heavier (more dense) fuels, like diesel, have higher heating values on a volume basis. Since space is at a premium in most aircraft, the amount of energy contained in a give quantity of fuel is important. A fuel with high volumetric energy content maximises the energy that can be stored in a fixed volume and thus provides the longest flight range.

There are currently two main grades of turbine fuel in use in civil commercial aviation: jet A-1 and jet A, both are kerosene type fuels. There is another grade of jet fuel, jet B which is a wide cut kerosene (a blend of gasoline and kerosene) but it is rarely used except in very cold climates.

Jet A-1 is a kerosene grade of fuel suitable for most turbine engine aircraft. It is produced to a stringent internationally agreed standard, has a flash point above 38 degrees centigrade (100 degrees Fahrenheit) and a freeze point maximum of minus 47 degrees Centigrade.

Jet A is a similar kerosene type of fuel, produced and normally only available in the U.S. It has the same flash point as Jet A-1 but a higher maximum freeze point (minus 40 degrees centigrade).

Jet B is a distillate covering the naphtha and kerosene fractions. It can be used as an alternative to jet A-1 but because it is more difficult to handle (higher flammability), there is only significant demand in very cold climates where its better cold weather performance is important. Courtesy : The Hindu

Why does an egg (with the shell) burst when cooked in a microwave oven?

Microwave radiation is generated in an electronic tube called a magnetron, and passes along what’s called a wave-guide into the oven cavity.

The microwaves are absorbed by foods — a characteristic that make them ideal for cooking. The microwave energy transmitted in a microwave oven is directed toward the centre of the compartment. The highest absorption factor for microwave energy is water. The water absorbs the energy and becomes agitated and this molecular level agitation is the friction that heats up food

When microwaved, different components in an egg expand at different rates, which can result in the egg exploding. White portion of egg contains a high proportion of water and yolk contains a high proportion of fat. Microwaved eggs can reach temperatures much higher than if they were simply boiled in water at 100 degrees Celsius. At these elevated temperatures, water inside the egg, mostly in the white albumen, vapourises — even as the albumen solidifies. If the pressure inside the egg exceeds the breaking strength of the shell, the egg will explode.

Using a wooden pick or tip of a knife to break the yolk membrane of an unbeaten egg before micro cooking to allow the steam to escape, can help prevent the explosion. Covering cooking containers with a lid, plastic wrap or wax paper encourages even cooking and (if we forget to prick the yolk) helps to confine the explosion Courtesy : The Hindu

How does a compact fluorescent lamp consume less electricity than conventional fluorescent lamps and bulbs?

Fluorescent lamps are based on the phenomenon of gas discharge between two electrodes at the ends of a glass tube. Generally these tubes contain a little mercury in the low-pressure vapour phase. When sufficiently large voltage is applied between the electrodes, some atoms of the vapour get ionised.

The process of ionisation usually starts with stray electrons and ions that are generally present in the vapour. The electron-ion pairs so formed get accelerated towards electrodes of opposite electrical polarity, gaining kinetic (speed-dependent) energy.

When they collide neutral mercury atoms, some of them are ionised and some are electronically excited. Excited (higher-energy) atoms release their energy in the form of electromagnetic radiation, part of which is in the visible and in the infrared regions of the spectrum. But it is rich in the invisible ultraviolet region.

A fluorescent light source has the inner surface of its glass tube painted with a material called phosphor. Zinc sulphide is the commonest example of a phosphor. But phosphors used in practice are complex mixtures of the sulphides and phosphates of barium, strontium and rare earth elements.

These phosphors have the property of absorbing ultraviolet component of the radiation and re-emitting a major fraction of the corresponding energy in the form of visible light. This enhances the lamp’s efficiency of converting electrical energy into visible light.

The ordinary fluorescent lamp works with a supply voltage of about 220 volt. Since the start of discharge process demands a little higher voltage, it also employs a starter and ballast (a choke coil) that together produce the desired voltage. On the other hand, the compact tube works at about 400 volt (constant), which is produced by a transformer arrangement embedded in its base.

Working at a higher voltage improves its efficiency of producing electromagnetic radiation. Another factor adding to its efficiency is the phosphor composition, which produces light richer on the violet side of the spectrum. This makes the light of a compact lamp somewhat more bluish than that of the ordinary fluorescent lamp. These newer phosphors are not yet being used in ordinary fluorescent lamps perhaps for cost reasons.

Higher efficiency means low consumption of electrical energy. A filament lamp has the lowest efficiency, because it is based on the fact that a material body heated to a high temperature emits radiation of all wavelengths. This radiation is richer in the infrared part of the spectrum and since there is no mechanism of converting this into visible light, it has poor efficiency. The three types of lamps may have a typical efficiency ratio of 8:6:3. Courtesy : The Hindu

What causes milk to rise up when we boil it?

Milk contains 87 per cent water, 4 per cent proteins and 5 per cent lactose (milk sugar). When we boil milk, the fat, sugar, proteins and minerals get separated. Since they are lighter than milk they collect on the surface in the form of cream.

During heating some amount of water gets converted into vapour and the bubbles of water vapour rise to the top but the heat is conducted away by the layer of water and by the fat droplets that have a higher boiling point than water.

The vapour gets trapped in the creamy upper layer. As the milk is heated further the water vapour expands and thick foam is produced on the top.

As the milk is boiled continuously the water, which boils at 100 degrees Centigrade, produces more water vapour and pressure builds up in the boiling milk so that the vapour pressure raises the creamy layer. So the milk pushes the creamy layer out and milk spills out. Courtesy : The Hindu

Why are we unable to see through a frosted glass?

A glass plate, which is polished on both the surfaces is ‘perfectly’ transparent to light and so one can see through it. However if one of the surfaces is sand blasted to get a frost glass, this rough surface would scatter almost all the light in all directions.

Therefore light entering one side of the glass plate is totally scattered and lost and thus is not able to pass through. So we cannot see through. If one of the surfaces is mirrored then too one cannot see through but in this case the light is not scattered but completely reflected off and one would then see it as a shiny mirror. Courtesy : The Hindu

Why does our mouth stink after a night’s sleep despite brushing before going to sleep?

Bad breath, or ‘Halitosis’ is a common problem, which often occurs due to bacterial activity in the mouth.

Although brushing is a good mechanical aid for maintaining proper oral hygiene, there are many factors that may cause morning bad breath or halitosis. Some people suffer from bad breath without knowing it, while others build up exaggerated fears about breath odour even though they do not have it. Halitosis, also termed ‘oral malodour’ is a foul or offensive odour emanating from the oral cavity. It is caused primarily by volatile sulphur compounds specifically hydrogen sulphide and methyl mercaptan which result from bacterial putrefaction of protein containing sulphur amino acids. These products could be involved in the transition from good oral health to gingivitis (inflammation of the gums or gingival) and then to periodontitis (inflammation of supporting tissues of the teeth).

Local source of mouth odour is mainly the tongue. Post nasal drip on the back of the tongue which occurs during sleep can also cause oral malodour in the mornings and can cause throat infections in some cases. A coated tongue is also said to be a cause of halitosis, due to excessive bacterial activity on the tongue. The causes of bad breath can be divided into

Intraoral sources(sources inside the mouth which can cause bad breath)

Extraoral sources(sources outside the mouth or anywhere else in the body).

Intraoral sources include retention of odoriferous food particles on and between the teeth, coated tongue and dehydration states which can cause dryness of mouth leading to oral malodour. caries

Habits like smoking, alcoholism and pan chewing, artificial dentures, insufficient salivary flow, gum problems, post nasal drip on the back of the tongue cause bad breath. Any infections of the respiratory tract like bronchitis, pneumonia can also cause bad breath.

Periodontitis (inflammation of the tissues surrounding the teeth) is one condition if left untreated can cause bad breath from accumulated debris and increased rate of putrefaction of the saliva.

There are many ways to prevent halitosis or oral malodour. Getting teeth cleaned periodically in a dentist’s office is one such practice.

Dental flossing along with tooth brushing helps in removing debris from in between the teeth. Using a soft bristled toothbrush on your tongue, taking plenty of liquid, cleaning your mouth after eating or drinking milk products, fish, meat helps. If you are a denture wearer, soak the denture in antiseptic solution overnight.

Chlorhexidine, Listerine and triclosan mouthwashes are available in the market that can be used after consulting your dentist.

Thus halitosis can be prevented by education of people regarding brushing techniques and other oral hygiene aids and motivation of people to make behavioural and habitual changes thereby avoiding unnecessary anxiety and apprehension. Courtesy : The Hindu

How does wheat flour become malleable and elastic when mixed with water?

Basically wheat flour does not contain any malleable or elastic characteristic materials. When water is added to wheat flour, a new product called Gluten is formed by hydration of wheat proteins. It causes the production of dough. Gluten contains water approximately 2/3rd of its weight. It forms about 90 per cent of the total protein of flour. It is stretchable product just like rubber. It also contains small quantity of fat, cellulose and minerals.

Gluten in turn contains protein fragments called Glutenin and Gliadin. These two confer the dough the elastic and malleable properties. When mixed together, as they are in dough, these two proteins form a tangle of strands that trap the gas. While gliadin in gluten confers mellowness and elasticity, the glutenin provides the structure. Greater the amount of gliadin, softer will be the gluten. Gluten is responsible for the rheological properties of dough because it forms the skeleton of the dough. High structured products like bread and bun require stronger quality of gluten while low structured products like biscuits and cakes do not require strong gluten. Courtesy : The Hindu

How do raw mangoes and bananas become ripe when treated with chemicals?

ANSWER I: The process of fruit ripening is chiefly regulated by a gaseous plant hormone called ethylene. Most fruits have elevated ethylene levels during ripening and sometimes just a peak in ethylene levels, just before the process of ripening begins.

Ethylene regulates the expression of several genes involved in fruit ripening so as to modulate the activity of various enzymes involved in the process of ripening. These enzymes act to soften the ‘skin’ of the fruit and also convert complex polysaccharides into simple sugars.

The chemical commonly used to ripen fruits commercially is ethephon (2-chloroethylphosphonic acid), which penetrates into the fruit and decomposes to ethylene. Incidentally, chemicals (e.g. calcium carbide) that produce acetylene, an analogue of ethylene, are also used in some places posing dangers of explosion and carryover of toxic materials to consumers.

Ethylene is induced by several cues such as higher temperature, wounding, disease etc. Higher levels of ethylene and enhanced respiration might contribute to ripening when stored at higher temperatures.

ANSWER II: The ripening signal of a fruit comes form a hormone ethylene. Production of ethylene turns on some genes that are transcribed and translated to produce other enzymes. These enzymes are responsible for the conversion of starch into simple sugar, degradation of chlorophyll and appearance of other new pigments like carotenoids, change in the skin colour and the breakdown of acid, making the fruit taste neutral.

Hardy nature of the skin loosens when pectin is broken-down by an enzyme pectinase. Conversion of larger molecules into smaller volatile substances causes an aromatic odour.

Natural process of fruit ripening is accelerated by using certain chemicals. Here, calcium carbide is used. When carbide is dissolved in water it produces acetylene, an analogue of ethylene, a natural fruit-ripening agent.

The ripening process is accelerated since acetylene imitates ethylene. Since the amount of carbide needed to ripen the immature fruit is more it makes the fruit become more tasteless and toxic. Presence of trace amount of arsenic and phosphorous in carbide makes the healthy fruits poisonous.

One can distinguish the artificially ripenened fruit by the uniform skin colour in fruits like tomato, mango, papaws, etc and in the case of banana, yellow colour fruit with dark green stem. Courtesy : The Hindu

What is the powdery deposit found on some fruits like grapes? What is its use?

The white deposit seen on grapes and most other berries is cuticular wax. Cuticle is the outermost layer covering the plant surface and plays a role in the plant’s interactions with its environment.

Cuticular wax is part of the cuticle in several plant parts in almost all plant species. It is usually embedded in the cuticle and in some plant species crystalline wax structures overlay this layer and appear as powdery white/grey deposit (for example, grapes and other berries).

Cuticular wax is also reported to play important roles in disease resistance against bacterial and fungal pathogens of plants and in plant-insect relationships.

Being reflective in nature, waxes are also thought to offer some protection against UV damage. In agriculture, waxes impede the uptake of foliar sprays without surfactants due their hydrophobicity (water repellent property). Courtesy : The Hindu

How is the speed of a computer measured?

Two important factors that determine the speed of a computer are the amount of data that the Central Processing Unit can process in a given period of time and the CPU’s clock speed.

The speed at which a CPU executes instructions is called the clock rate.

Every system contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks to execute each instruction.

The faster the clock, the more instructions the CPU can execute per second. Clock speeds are expressed in megahertz MHz or gigahertz GHz. Mega means million and hertz means times per second, 200 MHz is 200 million times per second (and 200 GHz is 200 billion times per second).

The internal architecture of a CPU has as much to do with a CPU’s performance as the clock speed. One common architecture is parallel processing. For example, while an instruction is being executed, the next instruction can be fetched from memory and decoded.

Instruction Prefetching is another idea where the CPU fetches the next instruction beforehand and places it in a queue for the execution unit to use the same.

The overall speed of a computer is also affected by the speed and size of the instruction/data bus. The instruction/data bus is the pathway for data communications between the computer’s CPU and the various components in the computer.

The computer’s bus has a certain size or width called the data path which is measured in bits and the speed of the bus is measured in MHz.

The larger the bus width and/or the faster the bus speed, the more data that can travel on it in a given amount of time.

Another factor affecting the speed is the size of the primary memory and cache. Increasing the size of the primary memory will speed up the performance if you run several applications at the same time or work with large files and documents. Cache is a small amount (normally less than 1 MegaByte) of high-speed memory residing on or close to the CPU. Cache memory supplies the CPU with the most frequently requested data and instructions.

Finally, effective interfacing of Input-Output devices to the CPU also increases the speed. Systems today use direct memory access (DMA) hardware wherein I/O device acts as a master and transfers large number of data to/from memory without intervention by the CPU. Courtesy : The Hindu

What is magnetic levitation? How does it work?

Magnetic levitation is the use of magnetic fields to levitate a (usually) metallic object. Manipulating magnetic fields and controlling their forces can levitate an object.

In this process an object is suspended above another with no other support but magnetic fields.

The electromagnetic force is used to counteract the effects of gravitation. But it has also been proved that it is not possible to levitate using static, macroscopic, ‘classical’ electromagnetic fields.

The forces acting on an object in any combination of gravitational, electrostatic, and magnetostatic fields will make the object’s position unstable.

The reason a permanent magnet suspended above another magnet is unstable is because the levitated magnet will easily overturn and the force will become attractive. If the levitated magnet is rotated, the gyroscopic forces can prevent the magnet from overturning.

Several possibilities exist to make levitation viable.

It is possible to levitate superconductors and other diamagnetic materials, which magnetise in the opposite sense to a magnetic field in which they are placed.

A superconductor is perfectly diamagnetic which means it expels a magnetic field (Meissner-Ochsenfeld effect). Other diamagnetic materials are commonplace and can also be levitated in a magnetic field if it is strong enough.Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field.

The induced magnetic moment is very small and in a direction opposite to that of the applied field. When placed between the poles of a strong electromagnet, diamagnetic materials are attracted towards regions where the magnetic field is weak.

Diamagnetism can be used to levitate light pieces of pyrolytic graphite or bismuth above a moderately strong permanent magnet. As water is predominantly diamagnetic, this property has been used to levitate water droplets and even live animals, such as a grasshopper and a frog.

Superconductors are perfect diamagnets and when placed in an external magnetic field expel the field lines from their interiors (better than a diamagnet). The magnet is held at a fixed distance from the superconductor or vice versa. This is the principle in place behind EDS (electrodynamic suspension) maglev trains. The EDS system relies on superconducting magnets.

A maglev is a train, which is suspended in air above the track, and propelled forward using magnetism. Because of the lack of physical contact between the track and vehicle, the only friction is that between the carriages and air. So maglev trains can travel at very high speeds (650 km/h) with reasonable energy consumption and noise levels Courtesy : The Hindu

Why is it easier to tear wet paper and not dry paper?

Tearing a paper involves overcoming the cohesive force between the cellulose fibres (of which paper is made). In the case of dry paper this force is high and hence tearing it is not very easy. However, the cohesive force that is of electrostatic origin becomes weakened in the presence of water.

This is akin to the way table salt (sodium chloride) dissolves in water due the weakening of the electrostatic attraction between the positively and negatively charged ions. In the case of paper, the effect becomes easily perceptible as paper is hydrophilic and absorbs water.

Once dipped in water, the water molecules can easily flow into the spaces between the fibres, weakening the cohesive force between them and making them susceptible to easy tearing. Courtesy : The Hindu

How are some insects able to walk on the surface of water?

ANSWER I :Water has a see-through film on its top layer that is created by surface tension. That means molecules of water are more likely to cling to other molecules of water than to something else. Some insects have a waxy coating on their body/feet. The surface tension of this coating [20 to 30 ergs/cm{+2}] is much less than water [72 ergs/cm{+2}] and hence water tends to bond to itself rather than wetting the insect’s feet and unless the insect is too heavy, it can remain on top of the water surface. For example, water striders and carpenter ants are so light that they can support themselves by spreading their weight on the surface tension of the water.

ANSWER II: Insects like the pond skater are able to walk on the surface of water mainly because of two factors. The first is their water-repellent (hydrophobic) cuticle. The cuticle of a pond skater is coated with wax to make it waterproof.

Again, the insects are able to maintain floatation or stand on the surface because a sufficiently large amount of its surface area is in contact with the water. The heavier the object, the more surface area is necessary to maintain floatation. As insects are very light weight the area of contact with the water surface is enough for it to prevent it from drowning. Courtesy : The Hindu

Why do wounds heal slowly in diabetics?

It is well known that chronic hyperglycaemia (raised blood sugar) impairs some host defence mechanisms and is associated with increased mortality due to infection in diabetic patients. Several studies have now confirmed that hyperglycaemia per se or the metabolic abnormality of diabetes is sufficient to explain the impaired immune response in patients responding to infections. There are multiple defects in the immune function in diabetics unlike people without diabetes.

There are normally 4000-11000 white blood cells per microlitre of human blood. Of these, the granulocytes (polymorphonuclear leukocytes, PMNs) are the most numerous. Acting together with lymphocytes and monocytes, these cells provide the body with powerful defences against viral, bacterial and parasitic infections.

The PMN granulocytes (a particular type of white blood cells) represent the host’s first defence barrier against bacterial agents. An abnormality in the antibacterial function of these white blood corpuscles is a very important factor. In diabetic patients these cells show various defects in their function.

PMN cells are attracted to the site of infection by various substances secreted by microorganisms. Cells from diabetic patients have an impaired movement, especially when the diabetes is poorly controlled.

The PMN type of white blood cells also show defect in ingestion of the microorganisms, which is an important step in fighting infections.

Uncontrolled diabetes also leads to a decrease in the killing activity of PMN. However, normalisation of blood glucose levels following intensive insulin therapy improves killing activity within 48 hours.

Diabetics also have other important defects in the immune system like reduction in the T lymphocytes (helper cells), a type of white blood cell. These cells normally help in cell-mediated immunity.

Serum immunoglobulin levels have been reported to be reduced in diabetic patients compared to normal subjects. Moreover, diabetics have reduced blood circulation to the extremities. This impairs wound healing particularly in the lower extremities. The antibiotics will be unable to reach the target tissues due to the poor blood supply. Courtesy : The Hindu

How do pharmaceutical companies arrive at expiry dates for medicines?

Most of the drugs used in modern medicine are organic molecules, which have, apart from their pharmacological properties, diverse physical and chemical properties. The utility of a drug depends on the availability of the active molecule in blood circulation for curing or controlling the disease. Due to various factors including the structure of the molecule, the formulation the packing and environmental factors these molecules undergo decomposition and degradation over time.

To determine the period over which the degradation will lead to reduction in the availability of the drug to levels below what is required, studies are conducted under what are called accelerated stability tests.

These tests simulate the long term effects of these factors on the stability of the active drug and the formulation in acute experiments lasting up to 45 days at temperatures of 45 degrees or more and humidity of 70 per cent or more. From the correlative data available, it is possible to predict the stability of the drug over long periods of even up to five years. Courtesy : The Hindu

What is the difference between computer monitor and colour television?

Computer monitor and colour television monitor use Cathode Ray Tubes (CRT). In all CRT monitors, the image is painted on the screen by an electron beam that scans from one side of the display to the other. A CRT is an evacuated tube containing an anode and a cathode that generates cathode rays (electrons) when operated at a high voltage.

The cathode rays produce an image on a screen when they strike phosphors on the screen, causing them to glow. The terms anode and cathode are used in electronics as synonyms for positive and negative terminals.

In a computer monitor the transitions in colour, intensity and pattern, as the beam scans across the screen are abrupt as areas of high intensity transform to areas of black as soon as text is placed on the screen. In television, the transitions tend to be very gradual.

Television relies on the brain’s ability to integrate transitions gradually in pattern that the eye sees as the image is painted on the screen. Each image on a television screen is composed of 525 lines, numbered from 1 to 525. The image drawing is a phased activity.

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During the first phase of screen drawing, even-numbered lines are drawn. During the next phase, the odd lines are drawn. The eye integrates the two images to create a single image. The scan is interlaced.

In the case of a computer monitor, the viewer is sitting within a foot or two of the screen, and is viewing a frequently changing text image. If a computer monitor used the same method of display as television, the many transitions would produce an annoying amount of flicker, because the brain is less able to integrate the dramatic transitions from bright to dark. Also, another problem is the inability of the monitor to paint the interlaced images exactly in between the lines from the preceding scan.

Text images make this much more visible to the eye at close range, and at the relatively slower speeds of an interlaced scan.

Therefore, computer monitors use a technique that does not try to interlace two images into one, but rather paints one continuous image at a time and is said to be non-interlaced. Consequently, computer monitors are designed to paint every line during every write of the picture to prevent flicker. This requires electronics that operate at twice the speed (or bandwidth) as that of a television and higher the bandwidth, higher the cost of the display. Courtesy : The Hindu

How are snake pits formed?

ANSWER I: Snake pits are a network of caves and crevasses formed by underground water and collapsed limestone serving as perfect locations for hibernating snakes. In cold countries, these pits protect them from very cold temperatures, which tend to dip as low as minus 40 degrees Celsius during winter. The snakes huddle themselves below the frost lines during harsh winter.

Snakes of the tropical countries, however protect themselves from the heat of summer by staying in pits, which are formed far below the ground level. These are protected underground from surface heat.

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ANSWER II : Most snakes do not make their own burrows, but inhabit the burrows made by other creatures, such as rodents. They also inhabit termite mounds.

Only a few species of snakes, such as sandboas and shieldtail snakes, are capable of making their own burrows, but even they prefer existing burrows, when available – Courtesy : The Hindu

How does a compact fluorescent lamp consume less electricity than conventional fluorescent lamps and bulbs?

Fluorescent lamps are based on the phenomenon of gas discharge between two electrodes at the ends of a glass tube. Generally these tubes contain a little mercury in the low-pressure vapour phase. When sufficiently large voltage is applied between the electrodes, some atoms of the vapour get ionised.

The process of ionisation usually starts with stray electrons and ions that are generally present in the vapour. The electron-ion pairs so formed get accelerated towards electrodes of opposite electrical polarity, gaining kinetic (speed-dependent) energy.

When they collide neutral mercury atoms, some of them are ionised and some are electronically excited. Excited (higher-energy) atoms release their energy in the form of electromagnetic radiation, part of which is in the visible and in the infrared regions of the spectrum. But it is rich in the invisible ultraviolet region.

A fluorescent light source has the inner surface of its glass tube painted with a material called phosphor. Zinc sulphide is the commonest example of a phosphor. But phosphors used in practice are complex mixtures of the sulphides and phosphates of barium, strontium and rare earth elements.

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These phosphors have the property of absorbing ultraviolet component of the radiation and re-emitting a major fraction of the corresponding energy in the form of visible light. This enhances the lamp’s efficiency of converting electrical energy into visible light.

The ordinary fluorescent lamp works with a supply voltage of about 220 volt. Since the start of discharge process demands a little higher voltage, it also employs a starter and ballast (a choke coil) that together produce the desired voltage. On the other hand, the compact tube works at about 400 volt (constant), which is produced by a transformer arrangement embedded in its base.

Working at a higher voltage improves its efficiency of producing electromagnetic radiation. Another factor adding to its efficiency is the phosphor composition, which produces light richer on the violet side of the spectrum. This makes the light of a compact lamp somewhat more bluish than that of the ordinary fluorescent lamp. These newer phosphors are not yet being used in ordinary fluorescent lamps perhaps for cost reasons.

Higher efficiency means low consumption of electrical energy. A filament lamp has the lowest efficiency, because it is based on the fact that a material body heated to a high temperature emits radiation of all wavelengths. This radiation is richer in the infrared part of the spectrum and since there is no mechanism of converting this into visible light, it has poor efficiency. The three types of lamps may have a typical efficiency ratio of 8:6:3. Courtesy : The Hindu

Why does it take a longer time to copy a file to a computer than delete it?

An Operating System (OS) is a program that acts as an intermediary between a user of a computer and the computer hardware.

Depending on the storage device being used, computers can store information in several physical forms. Each device has its own characteristics and physical organization, and hence different views of information are created. To unify all these views of information, a uniform logical view called a file is created.

A file is a contiguous set of data. It is the job of the OS to map this sequence of data into physical devices. The part of the OS responsible for this is the file system.

So the main task of the file system is to free the users of the details of storing of information in the physical devices. That is, when the storage device is changed, from disk to CD for example, the user still sees the same information.

In the most basic form, a file system consists of two distinct parts: a collection of files and a directory structure. The directory structure organizes and provides information about all the files in the system.

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Every file has certain attributes like its name, location (its address in the file system), size, access control information (whether the file can be read or written to or only executed etc), type (whether it is just a collection of data or has other special instructions), time, date and user identification.

If file A is to be copied to file B, then first a new file called B is created, next the contents of A are read and finally, this is written to B.

For this to happen, three steps are necessary. First, space must be found for B in the file system. Second, an entry for B must be made in the directory. The directory records the name of B and the location of B in the file system. Third, a request is sent to the OS to read the contents of A.

The OS finds the location information of A from the directory and reads the contents. Now to write to B, the OS again searches the directory for the address of B. Finally the content of A is written onto the space provided for B.

On the other hand if a file deletion is to take place, the process is much simpler. If file A is to be deleted, the OS just searches the directory for the named file.

Having found the entry, the space occupied by A is released so that it can be used by other files and the directory entry is erased.

As can be seen, the operations involved while copying a file are much more than those involved while deleting a file. Courtesy : The Hindu

A hen lays an egg every day. From where does it get the calcium required to make the eggshell?

A commercial layer that lays an egg almost everyday derives its calcium requirements entirely from the feed it consumes. The nutritional requirements of chicken have been understood completely over the years. Today’s layer bird yields 325 eggs in 365 days.

The calcium requirements are mainly contributed by the shell grit. The feed is a precisely formulated one and the nutritional requirements of the layer are fully met by the feed it consumes daily. Courtesy : Th

Why do doctors prescribe some medicines to be taken before and some after food?

When we take a medication, it is absorbed from various parts of our gut — some get absorbed in the stomach, some pass through the stomach into the intestines and get absorbed there.

The most important reason for timing a medication that is taken orally is to maximise its absorption so that more of the medication goes through the stomach into the blood.

Many medicines get absorbed better when food is not present and hence are taken on an empty stomach (an example is the hormone thyroxine which must be taken first thing in the morning). A few actually get absorbed better when food is present — an example of this is the antibiotic azithromycin. Some drugs are taken specifically with or after food because this may reduce the side effects of the drug on the stomach.

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For example pain medications and certain antibiotics all can irritate the lining of the stomach and therefore are best taken with or after food. Some drugs work in the wall of the stomach to reduce the absorption of food and this is the desired therapeutic effect — an example of this is the anti-diabetic drug called acarbose.

This drug must be taken with the first bite of food. Similarly other oral anti-diabetic drugs and the injection insulin are taken before food because that is when they need to act — just after you eat a meal. The long and short of it is that the timing of a drug has important effects on its absorption, action, potency and even side effects and it is a good idea not to leave the doctor’s office without being sure when you should be taking your medicine. Courtesy : The Hindu

Why does a mushroom shaped cloud form after a nuclear bomb explosion?

ANSWER I: When a nuclear weapon explodes, there is a rapid release of a large amount of energy within a small volume. This results in significant increase in temperature and pressure. The temperature may be a few tens of million degrees and pressure a few million times the atmospheric pressure. At this temperature, all the material present in the weapon will be converted into hot compressed gases.

Within a fraction of a millionth of a second of the explosion, the weapon’s residues emit large amounts of energy mainly in the form of X-rays. The surrounding atmosphere absorbs this energy. This results in the formation of a blazing, highly luminous, spherical mass of air and gaseous weapon residues called the fireball.

Within an extremely short time after the explosion, the fire ball from a high yield nuclear weapon will be about 130 metres across increasing to about 1700 metres in ten seconds.

The fireball expands rapidly engulfing the surrounding air. The ball of hot air is less dense than the surrounding air. It rises swiftly like a hot air balloon.

This rising column pulls up debris of the weapon, dust and moisture along with it forming a cloud. As it moves up, it cools gradually and reaches about 10 km where the atmosphere is extremely stable.

The ball of air mass moving up does not have enough energy to penetrate this stable layer. It flattens out. As the relatively warmer layers at the bottom push up, the top layers spread laterally and equally in all directions, and the cooler denser layers descend at the edges, giving a distinct mushroom shape.

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ANSWER II: Atmospheric nuclear explosion leads to sudden formation of a massive fireball near the ground, setting aflame whatever is in its vicinity. Since the fireball is very hot and thus less dense than the surrounding air, it rises very quickly. The massive updraft due to the rapidly rising fireball leaves a column of low-pressure. This acts as a chimney, sucking in smoke, dust and debris from the surroundings. This forms the stem of the mushroom.

At first the mixture of hot air and dust rises vertically, forming the column of the cloud. But as the hot cloud meets the colder air at higher altitudes, it slowly cools. Eventually the cloud reaches the temperature of the surrounding air and ceases to rise, but spreads horizontally along air levels at the same altitude, which are at the same temperature. This forms the cap of the mushroom.

The smoke, dust and debris gushing into the central column cause toroidal eddy currents in the horizontally spreading hot cloud. This introduces curling under the cap of the mushroom. Mushroom clouds are most commonly associated with nuclear weapons. However, any massive explosion capable of creating the same conditions would produce a mushroom cloud. Volcanic eruptions are typical natural mushroom clouds. Courtesy : The Hindu

Is sweat examined as a clinical sample like blood, urine and sputum?

Sweat analysis is used in clinical medicine for the diagnosis of a genetic disease called Cystic fibrosis (CF). Sweat is collected from the flexor surface of forearms from infants who are more than two weeks old and weigh more than 3 kg.

Sweat is collected on pre-weighed sodium chloride free filter paper or Wescor disposable collectors. After collection all precautions must be taken to avoid evaporation of the sample. If the test could not be done immediately, the sample can be stored at 4{+0} C, but for not more than 72 hours.

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For the diagnosis of Cystic fibrosis, concentration of chloride in the sweat is estimated by colorimetry. A Chloride concentration of more than 60 mmol/L supports the diagnosis of CF. Courtesy : The Hindu

Why do pregnant women like eating tamarind and raw mangoes?

Craving for unusual food (and some non food items like ash called pica) is considered as the first sign of pregnancy. In reality, although some women do get strong cravings, many do notNo one knows for sure what causes food cravings. Many women find that their senses of taste and smell are changed by pregnancy. For example, some women experience an odd metallic taste in their mouths very early in pregnancy (maybe the first sign of pregnancy for an ‘experienced’ mother); others find that taste and smell are dulled. It is possible that these changes affect food likes and dislikes.

Some people think that cravings happen in response to temporary deficiency of specific nutrients. There is probably some truth in this, but it is not the whole story. We only need minute quantities of each vitamin and mineral — certainly not enough to justify a continual craving for just one food. For some women, food cravings may be a conscious or subconscious response to emotion.

They may crave a favourite childhood food, or a food that is of special significance to their religion or culture. Craving unusual foods may also be a private way of marking the special state of being pregnant.

Rather than develop a food craving, many women find they suddenly go off certain foods or drinks like fried foods and coffee.

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This is often related to pregnancy sickness, but may also be the body’s way of ensuring that they eat and drink wisely. Generally, there’s no harm in giving into food cravings, especially if doing so helps getting through phases like early morning sickness which can be pretty distressing. However this must be done in moderation.

Eating a lot of one food only means eating less of other foods and therefore running the risk of becoming deficient in important nutrient. A craving for non-food items — such as ash or soap or toothpaste — is known as ‘pica’.Pica is potentially very harmful if indulged in and must be resisted.

Also, substances like soaps and ash may prevent the absorption of nutrients and other food substances. Courtesy : The Hindu

Why does the reception of a transistor become clear when the antenna is touched?

Radio frequency region of electromagnetic spectrum spreads from few Kilohertz to few thousand Mega Hertz .

The geometry of the Human body allows the limbs, head and torso to act as 3-dimensional antennas. The resulting effect can be called antenna factor. It amplifies the signal as high as five times the signal one may receive with other type of antennas like monopole, dipole and the like.

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We can see this effect in any radio frequency receiving instrument, such as, oscilloscope in any electronic lab or more commonly a transistor radio.

If one grabs the tip of antenna or touches the body of any transistor, the signal received multiplies several-fold and the reception improves. Courtesy : The Hindu

Why are antibodies not produced against sperms by the female’s immune system?

Some women do develop antibodies to sperm. This can be confirmed by doing tests on the serum (blood) for anti sperm antibodies or by doing sperm-cervical mucus (secretion from the neck of the uterus) interaction test.

In 25 per cent of infertile women and even in some fertile/pregnant women anti sperm antibodies are demonstrable. Why some women develop and others do not develop anti sperm antibodies is difficult to explain.

Sperms are foreign to both the man who produces them and the woman who receives them. In normal life, in normal men the sperms are kept away from the blood stream by the blood-testis barrier formed by the Sertoli cells in the testes.

This barrier is as strong as the blood brain barrier. Breach of this barrier, as occurs with infections or injury, may lead to the formation of anti sperm antibodies in men. Besides, semen also contains immune-suppressive agents secreted by seminal vesicles (accessory structure).

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We can see this effect in any radio frequency receiving instrument, such as, oscilloscope in any electronic lab or more commonly a transistor radio.

In normal women, sperms are deposited in the vagina and they gain access to the cervix and uterus within minutes. The acidic environment in the vagina kills the remaining sperms. Under normal circumstances the sperms do not gain access to the blood stream and hence do not lead to an immune response.

The possible explanations as to why some women develop anti sperm antibodies are:

– The breach of the blood tissue barrier in the women as occurs in vaginal injuries and possible exposure of the women to sperms in sufficient quantities.

– Each woman’s immune response is individualistic and varies from person to person.

The precise role of anti sperm antibodies in causation of infertility is not clear. Some believe anti sperm antibodies can be the cause of infertility both in men and women. Courtesy : The Hindu

Why are we unable to walk straight and tend to lose our balance when we walk with our eyes closed?

ANSWER I: When one wants to walk in a straight line the brain takes a visual reference point and uses this reference point to maintain the movement in a straight line. In the absence of a visual reference point the brain is unable to ascertain the exact direction in which the body is moving and hence most of us will be unable to walk in a straight line with our eyes closed.

However visual reference is not the only mechanism of maintaining balance or direction in our movements. We can judge the direction of movement very accurately with the balance sense from the balance mechanism in our inner ear and by kinesthetic sense, which is sensations we derive from our muscles, joints and ligaments.

Both these sensations will tell us very accurately as to the balance and direction of movement and position of the body at any point of time. This is highly developed in acrobats, gymnasts and ice skaters. They would be able walk in a straight line even with their eyes closed.

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ANSWER II: Human balance is maintained by three pillars namely vestibular system — balance organ in the inner ear and its connections — eye and proprioceptors in the joints of the body. Man can maintain balance with any two pillars but not with one pillar alone. Imagine a blind man who can walk without losing balance.

If the same person develops any disorder in the vestibular system or proprioceptive system, then he cannot stand or walk. Similarly if a normal person develops a disorder in the inner ear or proprioceptive system and tries to stand with eyes closed and feet together, he will lose balance. Courtesy : The Hindu

Why are diesel driven vehicles noisy?

Diesel engines are inherently noisy because of the auto-ignition of the initially formed mixture of fuel-vapour and air, which causes rapid rate of pressure rise producing the characteristic noise. This abnormality is due to the inborn feature of a diesel engine, which uses a high compression ratio to obtain high fuel efficiency and a high compression-temperature for ignition of the fuel injected into the cylinder at high pressure. In a diesel engine, unlike a petrol engine, the air and fuel do not mix outside the engine.

Air is compressed to a high compression ratio leading to high fuel efficiency, and also to a high compression temperature to initiate combustion. They just meet inside the combustion chamber for a brief period, while all the processes of mixture formation like fuel-jet break-up, evaporation and mixing should take place within a short time called ignition delay period. Combustion follows this after the initially formed fuel-air vapour auto-ignites with a noise, forming the sources of ignition (chemical spark plugs if you wish to call) for the bulk of the fuel remaining. Diesel engine can be made less noisy by using common rail high-pressure injection system and electronic control. Courtesy : The Hindu

Double cross hybrids are obtained by crossing two different hybrid plants. While these seeds might still have hybrid vigour, there is genetic variation between siblings in the double cross hybrid population. This is why the double cross hybrids do not perform as good as single cross hybrids. Earlier, use of less vigorous female parents in the production of single cross hybrid seeds led to low hybrid seed yields and higher seed production costs. The double cross hybrid method was developed to overcome these problems while retaining hybrid vigour. However, due to very good selection processes over the years, parental lines with good seed yields have been identified for generating single cross hybrid seeds. Courtesy : The Hindu

Why does a battery operated transistor make noise when a nearby tube light is switched on?

A conventional fluorescent lamp while switching on/off generates electromagnetic waves with frequency around 1400 kilo-hertz lying in the medium wave frequency region. Hence this can be considered as a mini radio-frequency generator.

Transistor radios (radio receiver to be more precise) operating especially in the medium frequency can pick-up this radio-frequency interference in the same fashion as they do while switching an ordinary electrical switch on/off. In particular this phenomenon is more pronounced in fluorescent lamps employing glow-switch starters operated to initiate the electrical discharge process inside the column of the fluorescent lamp.

This interference has profound dependence on the distance between the fluorescent lamp and the radio receiver, which varies as inverse square of the distance between them. This interference can also propagate via electrical connections leading to main cables so that this can travel longer distances.

Radio receivers can be made to overcome this interference by proper grounding or constructing an antenna of suitable design and length. That is why a radio operating in a properly grounded main electrical system does not pick-up this interference.

Another way to overcome this interference is to connect a small capacitor across the lamp terminals along with stabilisation of self-inductance (from the choke coil of the ballast). Hence in order to overcome this interference from radio waves it can be seen that a small capacitor is connected across the terminals of the glow-switch starter and the combination is put inside a canister for being used in fluorescent lamp fitting. Courtesy : The Hindu

Why do we see rainbow colours on a CD?

Display of colours by a CD can be understood in terms of the working of a plane optical reflection grating. It is a flat optical device whose surface is ruled (striped) with a set of closely and uniformly spaced lines, such that light is reflected by the gaps and absorbed by the lines. , When light falls on a plane reflection grating, it is scattered in all directions by each of its reflecting stripes. These waves from individual gaps are termed wavelets. When we look at the grating from a distance, wavelets from different stripes travel different distances to reach the retina of our eye. Their crests (or troughs) do not reach a given point at the same time. Usually crests of some wavelets and troughs of others reach a point. Troughs have the property of partially or totally nullifying crests and vice versa, depending on their strengths. In this case the wavelets are said to interfere destructively.

But for certain orientations of the grating, it so happens that troughs (or crests) of all wavelets reach a point together, enhancing the effect of each other. The wavelets are then said to interfere constructively. Ordinarily, when light falls on a grating, wavelets corresponding to all wavelengths (or colours) are sent out by the reflecting gaps. Since the conditions of constructive interference hold good only for some particular wavelength, light intensity at the receiving point is exceptionally high only for that wavelength. Light from the grating from the related direction is thus rich in the corresponding colour. Similarly light from slightly different direction is rich in another colour. A CD has a data recording track, which spirals from its outer periphery to the inner circular boundary. This takes many tens of thousand rounds about the CD’s centre. When examined along a radius of the CD, it is found to have a structure similar to that of a reflection grating — a set of almost straight tracks running perpendicular to the radius and separated by gaps. Therefore, like a grating the CD also displays colours. Courtesy : The Hindu

What is Nucelar Winter?

Nuclear explosions trigger a horrendous chain reaction. The instantaneous outcome is the thermal and blast effect annihilating everything in and around the area. The mushrooming cloud due to the explosion rises high into the stratosphere, spreading out vast quantities of soot and radioactive debris. Some of the debris fall back to the ground as rain out. The soot and other particles suspended in the atmosphere would block sunlight and lower the global temperatures steeply to subzero levels, ushering in wintery conditions over the planet. This sequence of events has been termed as “Nuclear Winter”. As a consequence, photosynthesis would stop leading to the destruction of all green plants.

Subsequently oxygen regeneration would cease and carbondioxide would accumulate. Earth’s radiation balance and heat budget would get altered leading to drastic changes in the global circulation pattern. the seasonal monsoons and tropiacl rains may disappear. the duration and extent of the nuclear winter scenario would depend on the location, season and intensity of the explosion. Courtesy : The Hindu

How is heat suddenly generated to the extent of 50,000 Fahrenheit during lightning?

Lightning is essentially an electrical discharge through gases. During the course of formation and segregation of clouds, some clouds lose electrons and acquire positive charge and others collect those electrons and become negatively charged.

Due to the electrostatic repulsion of similar charges, the static electricity is condensed more on the surface zones of the clouds. During rain, the clouds move very swiftly causing frequent close encounters. When clouds holding positive and negative static electrical charges approach one another, they constitute to form capacitors regionally.

A capacitor discharge its accumulated charge once its potential and the charge accumulated reach their limits. The discharge is sudden and occurs in a short span of time. Essentially, the situation is like a built-in high voltage CR (Capacitor-Resistor) circuit in which charge flows(discharges) through the clouds(resistor) once the capacitor is maximally charged.

During the course of the discharge that takes place in ( say t) seconds, there is a current I, flowing across the clouds which have a high potential difference, V between them.

Under these circumstances, the electrical energy is converted into heat, which is quantitatively equal to iVt. Even if the time t is short, the voltage V and the current i are in scales of thousands and hence the heat liberated amounts to temperatures of thousands of degrees Fahrenheit.

The temperatures are greater than even those on the surface of the sun (10,000 degrees Fahrenheit). The heat liberated devastates molecules and particles of the discharged portions of the clouds into a plasma state, which emits bright polychromatic(white) radiation (lightning light) and sends intense pressure variations in the atmosphere that results in the exploding loud noise(thunders).

Since the discharge through charged capacitors(clouds) is sudden and the current and voltage are very large, the heat liberated reaches suddenly to een 50,000 degrees Fahrenheit during lightning.
Courtesy : The Hindu

How is the light produced when an object is burnt?

A chemical reaction is a simple rearrangement of atoms leading to formation of newer substances(products). Hence, to favour the rearrangement,breaking of bonds in the reactants and making of bonds between atoms in the products occur.

Due to this in every chemical reaction there is involvement of energy (liberation or absorption depending on the bond energies of the elements in the reactant and the products). The energy involved may be light, heat or electrical energy.

All combustions (burning) are chemical reactions of a fuel with oxygen in which carbon-hydrogen and oxygen-oxygen bonds are broken in the reactants (except hydrogen) and carbon-oxygen and hydrogen-oxygen bonds are formed in the formation of the products.

The bond energies of these atoms are in such a way that the energy liberated is always more than the energy consumed for the breaking of bonds. The net energy is liberated in the form of both light and heat. Courtesy : The Hindu

Diamond is a good thermal conductor. But it is an excellent electrical insulator. How?

Diamond crystal is a three-dimensional network of carbon atoms. All carbon atoms in the network are strongly bonded by carbon-carbon covalent bonds.

Therefore diamond crystal has a highly symmetric cubic structure. The carbon atoms in diamond are precisely aligned. Thus diamond is an ideal crystal. Atoms in the crystal lattices in solids vibrate.

These vibrations, called the atomic vibrations facilitate thermal conduction (transport of heat) in solids. In an ideal crystal, the lattices are so precisely aligned that they do not interact with each other.

Therefore an ideal crystal conducts better than a non-ideal crystal resulting in ideal crystals having good thermal conductivity, which is a measure of heat conduction. Diamond being an ideal crystal is thus a good thermal conductor.

Mobile electrons facilitate electrical conduction – flow of current in solids. There are no free mobile electrons in diamond crystal to ficilitate electrial conduction. Thus diamond is an excellent electrical insulator. Courtesy : The Hindu

What is the difference between dial up and broadband Internet connections?

The fundamental difference between dialup and broadband connections is the manner in which the connection is made from PC to the Internet.

A dialup service connects to the Internet through a phone line with a maximum speed of 56kbps.

Broadband refers to a connection that has capacity to transmit large amount of data at high speed. Presently a connection having download speeds of 256kbps or more is classified as broadband.

Broadband comes in a number of forms – depending how the data is delivered – for example via cable, satellite and most commonly using a telephone line where as a dialup service always connects to the Internet through a phone line.

While using a dialup connection, we need to pay for a local call every time we dial the Internet. In addition phone line is engaged while we are on the Internet. With a broadband connection, phone line (if existing phone line is used) can still be used while using the Internet and both the phone and the Internet work simultaneously and no dialup costs are incurred. Telecommunication systems were originally built to carry analogue signals. In a dial up connection, modems are used to translate digital into analogue signals and communicating with Internet.

However, analogue transmission between the subcriber and the telephone company is a bandwidth bottleneck. Dialup connection speeds make it more difficult to view certain types of media, such as video, and it can take much longer to download and open emial attachments, play online games and so on.

In an broadband system, digital data does not have to be converted into analogue. it uses a different part of the line’s frequency spectrum, offers much wider bandwidth 9more lanes) and does not interfere with the use of the line for voice transmission. When connected to the Internet, such a connection allows surfing or downloading much faster than a dial-up connection. Dialup connection users a built-in modem to connect and does not require a special router, whereas broadband requires a special router or modem.

In terms of security for attack, dialup is more secured then broadband, Broadband users need to use a firewall to keep the computer “invisible” to the outside. Courtesy : The Hindu

When a lighted matchstick is shown before another light source, the shadow of the matchstick is formed on a screen but not the shadow of the flame. Why is it so?

A shadow is a lightless (dark) region formed beyond an opaque object in the direction opposite to the source of light. An opaque object that comes in the way of light prevents the light that is due to fall beyond it resulting in the formation of shadow.

When a lighted matchstick is shown before a source of light, the matchstick, being opaque obstructs the light from the source and acts a shadow of it on a screen.

The flame of the matchstick itself is a source of light. The flame throws its own light to fall on the region beyond it and cannot prevent the light from the other source too. Hence the shadow of the flame is not formed. Courtesy : The Hindu

Why are fishes not able to survive in distilled water?

Take a fresh grape fruit and keep it in distilled water for an hour. it is stouter than before. Another fresh grape fruit kept in salty water for an hour will appear slim and wrinkled. The grape has dissolved minerals,sugars and other ingredients in its juice. The skin of the grape is a semi permeable membrane across which water can diffuse from one side to the other through osmosis.

When the grape is kept inside distilled water, the concentration(salinity) of juice in the grape is higher than that of water and water moves osmotically from outside the grape to inside. Hence the grape appeared stouter. the reverse happened in the case of salty water.

The skin of the fish is like the skin of the grape fruit. If the fish is in distilled water, there is an osmotic flow of water from outside the fish to the inside because the salinity of the fish body is higher than that of water. Thus there is danger of dilution of the body fluids of the fish or at worst that of being blown out if the fish is to be in distilled water for a very long period of time. Courtesy : The Hindu

Tertiary structure of egg white protein is due to hydrophobic interactions and hydrogen bonding. They also contain Cysteine amino acid, which has sulfhydryl group (SH).

These sulfhydryl groups form covalent disulfide bonds and hold 2 distant sections of proteins in close proximity. Disruption of the tertiary structure (or 3 dimensional structure) due to heat, chemicals or acidity is called “denaturation”.

When we heat an egg, the, heat breaks the intermolecular forces and the tertiary structure gets broken. The proteins unfold from their nature folded structure and precipitate forming a white solid mass. Courtesy : The Hindu

What is the powder like material found on the wings of butterflies? What is its use?

As the order name implies, the powder like materials found on the Butterfly wings are called scales.

Butterfly wings have two membranous layers which are made up of chitinous materials. Wings are nourished by a number of tubular veins which play a significant role in oxygen exchange.

Like all other insects,butterflies also have two pairs of wings, viz forewings and hind wings. The wing surfaces are generally covered with unicellular,setae(hair) like or flattened, overlapping scales. Scales are outgrowths of the body wall and they are of different colours.

There are two fundamental mechanisms by which colous are produced on butterfly wings. the ordinary colour, the first one, is due to the presence of chemical pigments, which absorb certain wavelengths of the light and transmit or reflect others.

The second colour, which is known as iridescent colour, is produced by the interference of light due to multiple reflections within the physical structure of a material and thus most of the butterflies exhibit brilliant iridescence on their wings.

The scales have different functions such as attracting the opposite sex for mating,warning the predators and hiding with the background of environment (camouflage).

Some male butterflies have scented scales on their forewings,which release the pheromones to attract their mates. Courtesy : The Hindu

Why do our eyelashes and eyebrows never continue to gow unlike hair on our head?

Answer 1: The cilia or eyelashes are hairs situated on the margin of the lids. They are dispensed in two rows, totalling about 100-150 cilia in the ipper lid and half the number in the lower lid.

The pigmentation of the cilia is deeper than that of the scalp hair throughout adult life.

The average life of each cilium is from 3-5 months after which it falls out and a new one grows in to take its place. If the cilia is pulled out the new one replacing it reaches full size in about 2 months. Since the life of the cilia is only 3-5 months, it does not grow as long as scalp hairs.

Answer 2 : Small organs in the skin, called follicles produce hair. All follicles go through a three-stage cycle- anagen is a period when the hair grows actively; catagen is marked by a short phase during which growth winds down; and finally telogen is the stage of rest. The cycle is completed at the end of telogen and the hair falls and a new hair begins to grow.

Scalp hairs (hairs on the head) have the longest anagen period – four to eight years during which they grow and have just two to four months of rest stage.

Eyelashes, arm hair, and most other hairs on the body have significantly shorter growth periods of one to six months, followed by a 2-4 month period of rest.

That is why these hairs are shorter and appear to grow to a fixed length. Thus the length of time that the hair is able to spend growing during the growth phase controls the maximum length of the hair. The Hindu

ackfruit is the only fruit that grows also from the tree trunk. What makes this possible?

The jackfruit tree bears fruits in the trunks or near the base of older branches from where the female flowers emerge in the first place. Given that jackfruit is the heaviest among the tree borne fruits, reaching up to 35 kg in weight, it is possible that the trees bear them in the trunk or older branches that are strong enough to hold the fruit.

Another example is the durian tree, which is commonly found in south-east Asia. Durain fruits can weight up to 4 kg and emerge in large clusters from the trunk. Both jackfruit and durain have thick pedicels that hold these large fruits. Jackfruit trees bear male and female flowers in separate flower – heads.

The male flowers appear in new growth among the leaves above the female flowers.

Female flowers appear on short, stout twigs emerging from the base of the trunk or large branches; sometimes even from the base of the tree under the soil.

Durain flowers appear as a cluster and have bisexual flowers borne on short, thick twigs. The stigma (female part) matures much earlier than the another bearing stamens (male part) enabling cross-pollination. Courtesy : The Hindu

Origin: The jackfruit is believed indigenous to the rain forests of the Western Ghats of India. It spread early on to other parts of India, southeast Asia, the East Indies and ultimately the Philippines. It is often planted in central and eastern Africa and is fairly popular in Brazil and Surinam.

Adaptation: Jackfruit is adapted to humid tropical and near-tropical climates. Mature trees have survived temperatures of about 27° F in southern Florida, but these were frozen to large limbs. Young trees are likely to be killed at temperatures below 32° F. Unlike its relative, the breadfruit, the jackfruit is not injured by cool weather several degrees above freezing. There are only a dozen or so bearing jackfruit trees today in southern Florida, and these are valued mainly as curiosities. There are also several trees planted in the Asian exhibit at the San Diego Zoo. What they will do or how high they will grow remains a question. The tree is too large to make a suitable container-grown plant.

DESCRIPTION

Growth Habit: The jackfruit tree is handsome and stately. In the tropics it grows to an enormous size, like a large eastern oak. In California it is very doubtful that it would ever approach this size. All parts contain a sticky, white latex.

Foliage: The leaves are oblong, oval, or elliptic in form, 4 to 6 inches in length, leathery, glossy, and deep green in color. Juvenile leaves are lobed.

Flowers: Male and female flowers are borne in separate flower-heads. Male flower-heads are on new wood among the leaves or above the female. They are swollen, oblong, from an inch to four inches long and up to an inch wide at the widest part. They are pale green at first, then darken. When mature the head is covered with yellow pollen that falls rapidly after flowering. The female heads appear on short, stout twigs that emerge from the trunk and large branches, or even from the soil-covered base of very old trees. They look like the male heads but without pollen, and soon begins to swell. The stalks of both male and female flower-heads are encircled by a small green ring.

Fruit: Jackfruit is the largest tree-borne fruit in the world, reaching 80 pounds in weight and up to 36 inches long and 20 inches in diameter. The exterior of the compound fruit is green or yellow when ripe. The interior consists of large edible bulbs of yellow, banana-flavored flesh that encloses a smooth, oval, light-brown seed. The seed is ¾ to 1-1/2 inches long and ½ to ¾ inches thick and is white and crisp within. There may be 100 or up to 500 seeds in a single fruit, which are viable for no more than three or four days. When fully ripe, the unopened jackfruit emits a strong disagreeable odor, resembling that of decayed onions, while the pulp of the opened fruit smells of pineapple and banana.

There are two main varieties. In one, the fruits have small, fibrous, soft, mushy, but very sweet carpels with a texture somewhat akin to a raw oysters. The other variety is crisp and almost crunchy though not quite as sweet. This form is the more important commercially and is more palatable to western tastes.

CULTURE

Location:

The jackfruit tree should have a well-drained, frost-free location that is sunny and warm.

Soil: The jackfruit flourishes in rich, deep soil of medium or open texture. Planting on top of an old compost heap would be ideal. The faster one can force a tropical plant to grow, the better the chance of keeping it alive. The tree needs the best drainage and cannot tolerate “wet feet”.

Irrigation: The tree will not tolerate drought. Water frequently during warm months and warm periods in cooler months. Less water is necessary during colder weather.

Fertilization: The jackfruit’s requirements are not known, but frequent, weak solutions of all-purpose fertilizer will speed the plant’s growth without causing burn. In the regions where it is commonly grown, it succeeds without much care from man, the sole necessity being abundant moisture.

Frost Protection: Although mature jackfruit trees will take several degrees of frost, it is prudent to provide young plants with overhead protection if possible and plant them on the south side of a wall or building. Small plants should be given complete protection with a covering on cold nights and even a light bulb if possible.

Propagation: Propagation is usually by seeds, which can be kept no longer than a month before planting. Germination requires 3 to 8 weeks. The seedlings should be moved when no more than 4 leaves have appeared. A more advanced seedling, with its long and delicate tap root is very difficult to transplant successfully. Cutting-grown plants and grafted seedlings are possible. Air-layering is common in India.

Pruning: Little or no pruning is required other than to remove any dead branches from the interior of the tree, so that sufficient light is obtained for the developing fruit.

Pests and Diseases: A variety of pests and diseases afflict the jackfruit tree and fruit regions where it is commonly grown. In California the white fly is a minor pest.

Harvest: Jackfruits mature 3 to 8 months from flowering. When mature, there is usually a change of fruit color from light green to yellow-brown. Spines, closely spaced, yield to moderate pressure, and there is a dull, hollow sound when the fruit is tapped. After ripening, they turn brown and deteriorate rather quickly. Cold storage trials indicate that ripe fruits can be kept for 3 to 6 weeks at 52° to 55° F and relative humidity of 85% to 95%. Immature fruit is boiled, fried, or roasted. Chunks are cooked in lightly salted water until tender and then served. The only handicap is copious gummy latex which accumulates on utensils and hands unless they are first rubbed with cooking oil. The seeds can also be boiled or roasted and eaten similar to chestnuts. In Southeast Asia dried slices of unripe jackfruit are sold in the markets. The ripe bulbs, fermented and then distilled, produce a potent liquor.

How does one control the movement of hot air balloons?

Hot air balloons rise ito the sky because of the fundamental property of the hot air filled in them; air when heated becomes lighter (less denser) than the surrounding cold air. The balloon does not have controls such as accelerator, steering or brake. It is driven by breeze and so there is no control over the flight path. Ascending is by heating the air with the help of burners suspended beneath it. As a result, the balloon rises to find its equilibrium with the surrounding air. Descending is by releasing the hot air from the balloon. Hot air balloon enthusiasts venture out after studying the weather and making sure there are no strong winds. Courtesy : The Hindu

How does remote control in TV work?

In earlier days, remote controls wre based on ultrasonics (sound frequency above the audible range of frequencies). The controlling circuitry included a hand held transmitter 9that transmits ultrasound) and a TV-based receiver circuit. Electronic filter and stepper motors were used to allow/select certain frequencies and perform various functions depending on the key pressed.

But the recent remote controls use infra-red(IR) rays and a special binary (0 and 1) coding mechanism. The code, intensity and wavelength of the IR wave, help to select different functions. Depending on the key pressed, a signal is sent out by IR source say, an injetion laser diode(ILD). It generates a code in parallel format. This is converted to a series format by s shift register. This signal is received by photo-sensitive devices such as an avalanche photo diode at the receiver.

Here another shift register is used to convert the code back to a parallel form. This operates a one-of-n decoder, which selects one function from a set of “n” predefined functions and executes it. Courtesy : The Hindu

Why is the power of a loudspeaker expressed in watts?

Unlike sounds generated by human beings, and animals and materials, the sound output of a speaker is derived from an electrical signal. This electrical signal, like in other electrical appliances, represents the energy used or work done by a current flowing through it. This power, as we know,depends on the voltage, current and phase difference between the current and voltage, and is measured in watts. One watt is the energy or work done at one Joule per second. This scale makes measuriing of power output easy for commercial purposes. Courtesy : The Hindu

What makes the earth rotate?

The earth rotates simply because it has not yet stopped moving. The Solar System, and indeed the Galaxy, were formed by the condensation of a rotating mass of gas.

Conservation of angular momentum meant that any bodies formed from the gas would themselves be rotating. As frictional and other forces in space are very small, rotating bodies, including the Earth, slow only very gradually. Courtesy : The Hindu

What is the difference between a sodium vapour lamp, Which gives out a yellowish colour illumination, and a mercury vapour lamp that gives out a white colour illumination?

Answer I: The light in Sodium Vapour lamp is from an atomic emission process whereas in Mercury Vapour Lamp it is, finally, from fluorescence emission. The mechanism of light emission in a sodium vapour lamp is simple and straight-forward. The filaments of the lamp sputter fast moving electrons, which hit the sodium atoms(vapour) causing the valence electrons of the sodium atoms to excite to higher energy levels and the electrons thus excited relax by emiting the characteristic monochromatic bright yellow light(589nm).

The mechanism in mercury vapour lamp is more involved and sequential. The sputtered electrons from the filaments, after having been accelerated by high voltage, hit the mercury atoms.

The photons of this ultravilot light fall on the fluorescent layer on the inner walls of the tube and excite the molecular bonds of the fluorescent material to various electronic and vibrational energy states. Hence, the light from the mercury vapour lamp is white.

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Answer II: The basic difference between the two is, the former works by electric discharge (passage of electricity through sodium vapours at high/low pressure) while the latter works through the combined effect of electric discharge through mercury vapours and fluorescence from phosphors (luminescent materials). Although sodium vapour lamps produce much higher light output (about 90 lumens/watt) they cannot be used in lighting applications where colour-rendering property is very crucial. This is because most of the light emitted from a sodium vapour lamp is concentrated in the yellow part of the visible spectrum (around 580-590 nm)

On the other hand, a mercury vapour lamp is quite suitable for lighting applications. This is because, the mercury vapour lamp can feed almost the entire visible region (380-780 nm) of the human visual system. Conventional fluorescent lamps can also be called as low-pressure mercury discharge lamps. In this system, when electric discharge strikes mercury vapours held at low pressure ( a few mm of mercury) it produces a lot of ultravilot radiation dominantly at 254 nm inside the column of the discharge tube. This UV radiation when impinging on the white coating made of fluorescent materials coated inside the discharge column of the tube will generate white light(called daylight).

Light output from a fluorescent lamp is moderate (60 lumens/watt) while the colour-rendering index is high. Courtesy : The Hindu

Both Infrared and Microwave bands are invisible to the human eye. Then how are IR and microwave images from remote sensing satellites printed? How do they substitute the wavelenghts?

Both infrared and microwaves are part of the electromagnetic spectrum, which stretches from radio waves to gamma rays. each band of this spectrum corresponds to a small range of frequencies. each frequency is uniquely connected with an energy level.

The total spectrum is very wide. Our eyes respond only to a very small band called the visible band. However, different chemicals do react to certain higher or lower level of energy bands and hence can be used as photographic plates for detecting and measuring some of these radiations.

Satellites nowadays use sensors whose working principle is based on photoelectric effect, converting radiation reaching the sensor iinto electric charge, which can then be easily measured and processed.

Essentially, the energy detected over a given spectral band, whether it is in the visible, infrared or microwave band, is converted to an array of digits corresponding to the energy range and radioed to ground stations.

After receiving it, those values corresponding to the measured energy range (known as grey levels) are finnaly printed on a computer screen as a picture or as a conventional photograph. Courtesy : The Hindu

How does lightning affect TVs?

Lightning is actually a sudden discharge of high voltage and high current arisiing out of large viltage(potential) differences between charged clouds. These surges, in their path towards the earth, can strike power lines and antennae and pass through the wires to the terminal equipment such as TV. The huge currents and voltages, even though of short life, can damage the electrical components and electronic circuits which are usually designed for low power. The surges are so powerful that they can destroy the equipment even if they are off but connected to the mains/antenna. Courtesy : The Hindu

Soaps come in different colours. But why is soap’s lather always white in colour?

Lather or foam is nothing but a large collection of small soap bubbles. A soap bubble is , in turn, a very thin film of soap solution enclosing some air. Because of the low surface tension of soap solution, the film can stretch and spread and form innumerable bubbles with a very large total surface area.

Due to this, whatever slight tint is present in the thin film of the coloured soap solution gets subdued. Although a soap film is more or less transparent, the lather or foam looks white because the light striking this large collection of bubbles gets scattered. That is the reason why all kinds of lather or foam appear white. Courtesy : The Hindu

Is the mosquito a carrier of AIDS causing virus?

Acquired Immuno Deficiency Syndrome (AIDS) is caused by Human Immunodeficiency Virus (HIV). The presence of HIV in blood, semen and vaginal secretion of infected people promotes the spread of the infection through sexual contact (both heterosexual and homosexual), exposure to contaminated blood and blood products.

The virus can also be transmitted to the child from the mother. There is no concrete evidence to show that it is transmitted through insect bites.

Mosquitoes do transmit diseases like Malaria. In the case of AIDS they act as biological vectors and a certain period of time has to elapse for the parasite to become infective. The vector can transmit the infection only after the infectious agent undergoes a developmental process or multiplies in its body.

However HIV does not replicate in mosquitoes. Scientists at Centre for Disease Control, Atlanta have proved that even in mosquitoes injected with HIV contaminated blood, the virus survives only for one hour. Further, studies on epidemiology of AIDS have provided no evidence linking mosquitoes with disease. Courtesy : The Hindu

How many kinds of mosquitoes are there?

Throughout the world there are over 3,000 species of mosquitoes. Florida has 76 mosquito species from 13 different genera, 30 of which occur throughout the entire state. There are 14 species in Bay County. Each type of mosquito has a common name and a scientific name which includes a genus and a species name. For instance, the Asian tiger mosquito is the common name, while Aedes albopictus is the scientific name. Aedes albopictus is a container-breeding mosquito, and on our visits to residents homes this is the most common mosquito found.

What purposes do mosquitoes serve?

Mosquitoes are an important link in the food chain. Many animals depend on them as a source of food. During their aquatic stage, mosquito larvae provide food for the other aquatic insects such as, dragonfly nymphs and beetles, fish, frogs and other water-dwelling animals. As adults, mosquitoes are eaten by birds, bats, spiders, lizards and other insects. Mosquitoes do not feed on blood alone. The blood meal is taken by the female to produce eggs. Both male and females need liquid nourishment for food. Plants provide the source of liquid nourishment. Mosquitoes feed on plant nectar, honeydew, fruit juices and liquids oozing from injured plants. Because of this need for nourishment, mosquitoes are important pollinators of wildflowers during this feeding process.

Are mosquitoes attracted to some people more than others?

Yes. Mosquitoes are attracted to the carbon dioxide (CO2) emitted from the breath and pores of humans. In addition to CO2, some species of mosquitoes are attracted to certain fragrances and colors. During mosquito season it is recommended that people who wish to be less attractive to mosquitoes wear unscented products such as hair spray, soap, deodorant, etc. and light colored clothing.

Why can’t mosquito control programs spray during the day?

Mosquitoes are more active in the evening, and people are less active. The second reason is the spray will be lifted quicker from the ground due to rising air currents during the day. Daytime spraying is also not practiced to avoid killing beneficial insects.

When can I expect to see a spray truck?

When conditions meet the required criteria, you should see a spray truck every 5 to 7 working days (weather permitting). Adulticide spraying can vary from year to year due to environmental conditions, which include rainfall amount and tide changes.

Is the Spray harmful to people or pets?

The amounts of mosquito control pesticides that are sprayed out of the trucks are not harmful to people or pets. However, as with any pesticides, it is a good idea to keep exposure to a minimum. For this reason, children should not be allowed to follow the mosquito trucks as people often did in the 1940s and 1950s. Pets usually are repelled by the high pitch of the machine. Therefore, even if it seems that they are not spraying, the trucks should not be followed. Unless someone is very sensitive or allergic to pesticides, washing the skin with water is all that is needed. At the low insecticide dosage used, no symptoms should be experienced. People who are sensitive should call the office and notify us prior to any spraying.

Is it safe to eat vegetables or fruit from the garden after a mosquito control application?

Fruits and vegetables exposed to malathion at mosquito control rates can be safely eaten after washing the food to cleanse it of germs and microorganisms. In fact, malathion is registered by the EPA for the control of many insect pests on a wide variety of fruit and vegetable crops.

Is the mosquito a carrier of AIDS causing virus?

Acquired Immuno Deficiency Syndrome (AIDS) is caused by Human Immunodeficiency Virus (HIV). The presence of HIV in blood, semen and vaginal secretion of infected people promotes the spread of the infection through sexual contact (both heterosexual and homosexual), exposure to contaminated blood and blood products.

The virus can also be transmitted to the child from the mother. There is no concrete evidence to show that it is transmitted through insect bites.

Mosquitoes do transmit diseases like Malaria. In the case of AIDS they act as biological vectors and a certain period of time has to elapse for the parasite to become infective. The vector can transmit the infection only after the infectious agent undergoes a developmental process or multiplies in its body.

However HIV does not replicate in mosquitoes. Scientists at Centre for Disease Control, Atlanta have proved that even in mosquitoes injected with HIV contaminated blood, the virus survives only for one hour. Further, studies on epidemiology of AIDS have provided no evidence linking mosquitoes with disease. Courtesy : The Hindu

How many kinds of mosquitoes are there?

Throughout the world there are over 3,000 species of mosquitoes. Florida has 76 mosquito species from 13 different genera, 30 of which occur throughout the entire state. There are 14 species in Bay County. Each type of mosquito has a common name and a scientific name which includes a genus and a species name. For instance, the Asian tiger mosquito is the common name, while Aedes albopictus is the scientific name. Aedes albopictus is a container-breeding mosquito, and on our visits to residents homes this is the most common mosquito found.

What purposes do mosquitoes serve?

Mosquitoes are an important link in the food chain. Many animals depend on them as a source of food. During their aquatic stage, mosquito larvae provide food for the other aquatic insects such as, dragonfly nymphs and beetles, fish, frogs and other water-dwelling animals. As adults, mosquitoes are eaten by birds, bats, spiders, lizards and other insects. Mosquitoes do not feed on blood alone. The blood meal is taken by the female to produce eggs. Both male and females need liquid nourishment for food. Plants provide the source of liquid nourishment. Mosquitoes feed on plant nectar, honeydew, fruit juices and liquids oozing from injured plants. Because of this need for nourishment, mosquitoes are important pollinators of wildflowers during this feeding process.

Are mosquitoes attracted to some people more than others?

Yes. Mosquitoes are attracted to the carbon dioxide (CO2) emitted from the breath and pores of humans. In addition to CO2, some species of mosquitoes are attracted to certain fragrances and colors. During mosquito season it is recommended that people who wish to be less attractive to mosquitoes wear unscented products such as hair spray, soap, deodorant, etc. and light colored clothing.

Why can’t mosquito control programs spray during the day?

Mosquitoes are more active in the evening, and people are less active. The second reason is the spray will be lifted quicker from the ground due to rising air currents during the day. Daytime spraying is also not practiced to avoid killing beneficial insects.

When can I expect to see a spray truck?

When conditions meet the required criteria, you should see a spray truck every 5 to 7 working days (weather permitting). Adulticide spraying can vary from year to year due to environmental conditions, which include rainfall amount and tide changes.

Is the Spray harmful to people or pets?

The amounts of mosquito control pesticides that are sprayed out of the trucks are not harmful to people or pets. However, as with any pesticides, it is a good idea to keep exposure to a minimum. For this reason, children should not be allowed to follow the mosquito trucks as people often did in the 1940s and 1950s. Pets usually are repelled by the high pitch of the machine. Therefore, even if it seems that they are not spraying, the trucks should not be followed. Unless someone is very sensitive or allergic to pesticides, washing the skin with water is all that is needed. At the low insecticide dosage used, no symptoms should be experienced. People who are sensitive should call the office and notify us prior to any spraying.

Is it safe to eat vegetables or fruit from the garden after a mosquito control application?

Fruits and vegetables exposed to malathion at mosquito control rates can be safely eaten after washing the food to cleanse it of germs and microorganisms. In fact, malathion is registered by the EPA for the control of many insect pests on a wide variety of fruit and vegetable crops.

Does the change in mother’s food affect the baby?

Whatever the nursing mother eat will be secreted in her milk, but in insignificant quantities. Generally if the mother tolerates a particular food item well the baby also tolerates it well.

A normal well nourished mother secretes about 500 ml of milk daily for the first 6 months to one year and after that the quantity slowly comes down. Whereas an undernourished mother’s milk is insufficient in fats and vitamins and inadequate for the baby also.

Eating fishes and vegetables contaminated with pesticides may cause problems in the baby because of their secretion in the milk. Eating spices, condiments, chocolates, onions, tomotoes may cause loose stolls in the babies.But the problems are plenty in the baby of a mother who smokes, drink alcohol and abuses the drugs. Almost all the drugs are excreted in the breastmilk and they will have their effect on the body.

For medical reasons if the mother has to take certain drugs like anticoagulants, anti-cancer drugs, antithyroid drugs, radioactive drugs, purgative etc., seh has to stop feeding her baby as long as she is on those rugs. Courtesy : The Hindu

What is Radio Therapy?

Radiotherapy, also called radiation therapy, is the treatment of cancer and other diseases with ionising radiation. There are generally two types – internal radiotherapy and external radiotherapy. Internal radiotherapy is given in one of two ways; either by placing radioactive implants directly in a tumour or body cavity, or by giving a radioactive liquid, either through mouth or as an injection into a vain. Ionizing radiation deposites energy that injures or destroys cells in the area being treated (the “target tissue”) by damaging their genetic material, making it impossible for these cells to continue to grow. Although normal cells are also affected, they can repair themselves more effectively.

The damage to normal cells is usually temporary and has some unwanted side effects. Possible side effects include temporary or permanent loss of hair in the area being treated, skin irritation, tempory change in skin colour in the treated area, and tiredness. This therapy is used to treat localised solid tunours, such as cancers of the skin, tongue, larynx, brain, breast, or uterine cervix. It can also be used to treat leukemia and lymphoma.

External radiotherapy does not make you radioactive, and is perfectly safe. X- rays were the first forms of photon radiation to be used to treat cancer.

Linear accelerators and betatrons are used to produce high-energy X- rays. The higher the energy of the X- ray beam, the deeper the X – rays can go into the target tissue.

Gamma rays are another form of photons used (cobalt irradiation), in radiotherapy. Particle beam radiation therapy, which uses fast-moving subatomic particles like neutrons, pions, and heavy ions are also used to treat localised cancers. It is referred to as high linear energy transfer (high LET) radiation. Courtesy : The Hindu

Since clouds contain tiny water droplets, why are rainbows not permanently present?

On a rainy day, sunrays, which are polychromatic(with all the seven colours), fall on water droplets at a certain incident angle adn refract with certain other refractive angle because water is denser than air.

Since the line of incidence of the rays may not be collinear to the drop’s diameter, the angle of refraction, however, is different for different colours of the rays in order that each colour catches up with the other at the opposite side of the droplet (remember the frequency of a given colour is invariable irrespective of the medium and the velocity of all colours is same in a given medium).

In other words, a polychromatic ray gets dispersed into seven colours of the visible light as the light beam is refracted into the body of the droplet.

The colours, thus dispersed undergo total internal reflection on the opposite inner side of the droplet and reach the eye to enable us feel the virtual image of the rainbow.(In fact, the mechanism of appearance of the rainbow is more complex than this and there is a cooperative phenomenon that includes interference in space and time.)

However the extent of the resolution of the seven colours in the droplet depends greatly in the extent of the (path) length the rays cover in the droplet.

In a shorter track the ralative gap, after the run is less whereas ina longer track it is more.

In normal clouds, the droplets are too small to cause sufficient resolution of the colours and to enable total internal reflection and hence rainbow is invisible with dry clouds.

On a rainy day, the droplets are big enough to cause the resolution and total internal reflection of the clours to enable us to see the rainbow(also theyare numerous and closer ans t an appropriate viewing angle to allow the cooperative phenomenon.) Courtesy : The Hindu

How does the solar wind affect Earth?

Solar wind contains intense clouds of high energy particles which are produced by solar stroms. These clouds of particles affect Eart. These clouds are called coronal mass ejections. They reach the earth in three to four days.

The coronal mass ejections cause changes in the magnetic field of the earth when they collide with the field. They cause more changes to the magnetic field at times even at lower altitudes close to the ground when they leak through the field especially near the north ans south Poles. These changes can produce many problems with electrical equipment.

Not much light has been thrown on the way in which solar wind” plasma” invades the Earth’s magnetic field and seeps into the inner regions where the Van Allen radiation belts are located. Also, in the direction opposite the Sun, the Earth’s magnetic field is pulled way out into interplanetary space making it look like a comet. Many different electrical disturbances take place in this “geotail” region. These can accelerate partiles to high speeds and energies. All of this is made much more violent by the solar wind, especially the strom clouds that the Sun launches our way very often. Courtesy : The Hindu

How do icebergs form?

Icebergs are blocks of fresh-water ice that break off from glaciers and float out to sea. Glaciers are formed in polar regions where snowfall lasts for centuries, or even millennia, without entirely melting, and is eventually compressed into ice.

In the North Altantic, most icebergs originate from the tidewater glaciers of Western Greenland. Compressed snow becomes firm, a granular snow, transformed eventually by pressure into a dense ice. The weight of the icecap builds, causing the ice to flow as much as 60 feet a day through openings in the coastal mountains. Rising and falling tides cause slabs of ice to break off and form moving “rivers of ice”. Courtesy : The Hindu

Why is fire hot?

Chemical reactions can be either exothermic(heat liberation) or endothermic (heat absorption). Oxidation reactions are exothermic and reduction reactions are endothermic. Combustion is an oxidation reaction and hence is exothermic.

All liquid,solid and gaseous fuels contain any one of the three combustibles constituents viz, carbon, hydrogen ans sulphur. When a fuel is burnt the heat liberated makes the products of combustion hot. The products of combustion are carbon dioxide, water vapour ans sulphur dioxide. Along with these, the unused oxygen in the atmospheric air supplied for combustion and also the entire quantity of nitrogen which is the major constituent in the air are also heated. That is why fire is hot. Courtesy : The Hindu

How is sex determined in dioecious plants?

More than 90 per cent of flowering plants produce perfect flowers that have both male and female reproductive organs.

Of the remaining plant species, about half are monoecious, producing male and female flowers on the same plant and the rest are dioeceous, producing male and female flowers on separate plants. Plants have developed weveral interesting mechanisms for determination of sex.

Silene latifolia is the most well studies dioeceous plant for sex determination mechanisms. In this species, sex determination is by sex chromosomes similar to that inmay animals, males are XY and felames are XX.

In male and female plants, female and male reproductive organs do initiate respectively by are aborted early in flower development. The Y- Chromosomes are thought to carry genes that promote male development and suppress female development. A similar mechanism has also been reported in the bryophyte Marchantia.

Papaya can produce male,female and hermaphrodites depending on the genotype of a single sex determining locus. This locus is thought to be clustered with several genes that play a role insex determination.

Cucumber is usually monoecious producing female flowers at the top of the inflorescence ans male flowers at the bottom. It has been found that sex is determined by the concentration gradient of the plant hormone ethylene, which acts to promote female sex.

In maize, agradient of the plant hormone gibberellic acid regulats the emergence of the male and female inflorescences. Hormone gradients in these species are genetically determined by two or three different genetic loci.

IN addition to the above mechanisms, in the fern Ceratopteris, sex determination is epigenetically determined by a pheremone.

All individuals are hermaphrodites ans developed individuals secrete the pheromone so as to masculinise the surronding juvenile plants Courtesy : The Hindu

How does the camel walk in the desert easily?

The camel is dubbed the ‘ship of the desert’. It can adapt itself easily to the hot conditions due to various reasons. Its special adaptation features are its hump, long legs, long hair and special eyelids.

The hump enables it to store food. Long hair on its body helps it keep warm in the cold desert nights.

The long legs of the camel are strong and have powerful muscles allowing it to carry heavy loads for long distances. It walks at a medium speed. It has two toes on each foot. A hoof that looks like a toenail grows at the front of each toe. The camel walks on a broad pad that connects its two toes. This cushion like pad spreads when the camel places its foot on the ground.

The pad supports the animal on loose sand in much the same way that a snowshoe helps a person walk on snow. The pad enables the animal to firmly grasp the earth. The toenails protect the feet from damages resulting from a bump. In the camel both legs on the same side rise and fall together. This leg action produces a swaying, rocking motion. Taller animals like the camel snap into a rotary walk more often than short animals.

This helps them to shift the balance on one side of a body while the long legs on the other side are in a suspended phase. In the rotary motion on one side they put both legs forward and on the other side they are both back. Thick, broad sole pads and thick callosities on the joints of the legs and on the chest, upon which it rests in a kneeling position, enable it to withstand the heat of the desert sand. It is also able to close its nostrils against flying dust and its eyes are shielded by eyelashes.

The camel has three eyelids and two layers of eyelashes to protect itself from dust and sun. To protect their eyes, camels have long eyelashes that catch most of the sand when desert winds blow sand on to their eyes.

If sand gets into an eye a camel has a third eyelid to get it out. The extra eyelid moves from side to side and wipes the sand away. As the eyelid is very thin the camel can see through it. So a camel can find its way through a sandstorm with its eyes closed. Courtesy : The Hindu

How can we test the purity of honey?

Answer I :The purity of honey can be easily detected using different methods. One such test is the aniline chloride test. Here aniline chloride is first prepared and then used for testing. Three parts of aniline and one part of concentrated hydrochloric acid gives us aniline chloride.

A small ceramic vessel is taken and a small quantity of honey is placed in it. About 5-7 drops of aniline chloride is added to it and stirred well. If the honey is adulterated a crimson red colour appears.

In another method honey is taken in a test tube and equal quantity of water is added to it and stirred well. About 100 millilitres of this solution is taken and 5 ml of ether is added to it. This mixture is kept aside for some time in order to get a fine solution after stirring. The ether layer settling on the top is transferred to another small flat bottom vessel. The ether gets vapourised in a short while and to this resorcinol is added. This gives a red colour. This indicates that the honey has an adulterant.

In addition to all these tests an important factor to be highlighted is about the granulation of honey. One of the nutrients (sugar) in pure honey precipitates when it is subjected to cool weather. This precipitation gives an appearance of sugar crystals. The honey giving more sugar precipitates faster. Mostly this is mistaken for adulteration. But if the precipitated honey is kept in hot water it attains normal liquid state which shows that it has no adulterant.

Answer II: A cotton wick dipped in pure honey when lighted with a matchstick burns and shows the purity of honey. If adulterated, the presence of water will not allow the honey to burn, If it does, it will produce a cracking sound. Generally honey is adulterated by adding a syrup of jaggery. Pure honey does not dissolve in water but impure honey dissolves. So to test it mix a spoon of honey in a cup of water and find out whether it dissolves to check its purity. Courtesy : The Hindu

What is meant by ozonised mineral water?

Ozone is a blue gas with a relative molar mass of 48 and molecular formula of O{-3}.

It converts back into oxygen after its oxidising process. This makes it the most eco-friendly treatment known today.

Ozone is the ultimate in disinfection. When drinking water is treated with chlorine (chlorine is a highly carcinogenic chemical), the residual chlorine in water is also consumed along with the water.

On the other hand ozone, having half the life of only about 20 minutes, unreacted ozone reduces to oxygen, leaving no trace of toxicity in water.

The water is free from chlorine. Ozone reacts with impurities such as micro organisms including bacteria, virus, spores, mould and fungi. Chemicals such as chlorine neutralise them.

As ozone destroys all micro organisms and it removes disagreeable odours, the resultant water is absolutely safe, pure, fresh and healthy. Ozonised water is colourless and odourless.

The advantage of the use of ozone in water is that it does not leave a dangerous chemical residue like many conventional treating chemicals.

Then the generated ozone is bubbled through the water to be treated in a specially designed vessel to control rate of injection. The amount of ozone to diffuse in water depends on the

Why do lips become dry during winter?

Our skin is endowed with both cold and warmth receptors. There are more cold receptors than warmth receptors. Therefore peripheral detection of temperature mainly concerns detecting cool and cold instead of warm temperatures.

When the skin is chilled over the entire body immediate reflex effects are involved to increase the temperature of the body. The two important effects are providing a strong stimulus to cause shivering, with resultant increase in the rate of body heat production and promoting skin vasoconstriction to diminish the transfer of body heat to the skin.

The effects of hypothermia depend on whether there is whole body exposure or exposure of only body parts.

When the whole body is exposed, metabolic processes; particularly in the brain and medullary centres slow down, causing death, before apparent changes in the cells or local reactions will occur in the parts of the body.

When only parts of the body gets exposed to very chill temperature, the local reactions begin to appear. These reactions are chilling and freezing of cells and tissues leading to frost bite. The injury is in two ways. (1) Crystallisation of the intra and extra-cellular water causing physical dislocation within the cells, which is the direct effect. (2) The indirect effects are exerted by circulatory changes. Depending on the rate at which the temperature drops and the duration of the temperature, slowly developing chilling may induce vasoconstriction and increased permeability, leading to oedematous changes. This results in the dryness of the body skin and also lips.

When the drop in temperature persists for a long time atrophy and fibrosis may follow, which result in permanent circulatory impairment as well as tissue damage. Often gangrene follows thawing and the frostbitten areas are lost.

This we often experience in the lips by the appearance of infarction necrosis of affected areas even after the temperature begins to return towards normal. Courtesy : The Hindu

Why do houseflies rub their front legs together?

Housefly (Musca Domestica) is a common insect found in all places. It has a very short life span. Adult houseflies feed on human and animal food and waste materials and often use buildings as shelter.

The housefly is well adapted in structure and behaviour to transmit disease causing organisms from place to place.

The body of a housefly is covered with fine hairs and bristles that readily pick up filth particles.

At the base of each leg there is a cushion-like structure covered with granular hairs.A sticky secretion which excretes from the granular hairs gathers bacteria and other micro organisms which stick to the legs. In order to clean its body and the legs, houseflies rub their legs together. It is estimated that whenever a housefly rubs its legs, lakhs of bacteria are discharged from the legs for each rubbing. Courtesy : The Hindu

ow does a lightning arrestor work?

ANSWER I: Lightning, is a form of visible discharge of electricity between rain clouds or between a rain cloud and the earth. The electric discharge is seen in the form of a brilliant arc, sometimes several kilometres long, stretching between the discharge points. How thunderclouds become charged is not fully understood, but most thunderclouds are negatively charged at the base and positively charged at the top. However formed, the negative charge at the base of the cloud induces a positive charge on the earth beneath it, which acts as the second plate of a huge capacitor.

When the electrical potential between two clouds or between a cloud and the earth reaches a sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes ionized along a narrow path and a lightning flash results.

Many meteorologists believe that this is how a negative charge is carried to the ground and the total negative charge of the surface of the Earth is maintained.

The possibility of discharge is high on tall trees and buildings rather than to ground. Buildings are protected from lightning by metallic lightning rods extending to the ground from a point above the highest part of the roof. The conductor has a pointed edge on one side and the other side is connected to a long thick copper strip which runs down the building. The lower end of the strip is properly earthed. When lightning strikes it hits the rod and current flows down through the copper strip. These rods form a low-resistance path for the lightning discharge and prevent it from travelling through the structure itself. — The Hindu S & T Desk

ANSWER II: The lightning arrestor protects the structure from damage by intercepting flashes of lightning and transmitting their current to the ground. Since lightning strikes tends to strike the highest object in the vicinity, the rod is placed at the apex of a tall structure. It is connected to the ground by low-resistance cables. In the case of a building, the soil is used as the ground, and on a ship, water is used. A lightning rod provides a cone of protection, which has a ground radius approximately, equal to its height above the ground. Courtesy : The Hindu

Like ordinary paints do metallic paints also fade?

Metallic paints do fade. It depends on the quality and the type of the aluminium paste used. Usually in most of the metallic paints, the commonly used pigment is aluminium pigment in the form of paste.

Two types of aluminium pigments are available in the market. One is leafing, and the other is the non-leafing aluminium pigment.

The difference between these two is, the leafing aluminium pigment will not get dispersed (or dispersed partially) with the resin while mixing, whereas the non-leafing will get completely dispersed with the resin during mixing.

So, if the metallic paint contains the leafing aluminium pigment it will get faded over a period of time, whereas if it contains a non-leafing aluminium pigment it will not fade for a longer period.

Example: The street lampposts on the roads and highways which are coated with metallic paints appear dull after a short period of coating, whereas cars coated with metallic paints shine even after a long time. Courtesy : The Hindu

What is the difference between tv screen and computer monitor?

ANSWER I: Computer monitors are capable of accepting signals only from the central processing unit of a computer. Therefore they are unable to reproduce a colour image from a composite video signal whose waveform conforms to a broadcast standard (NTSC, PAL, D-MAC, etc.).

Computer monitors are fitted with connectors characteristic of data processing systems (eg. DINorDB9/15 also called MINI SUB D15Connectors) and do not have an audio circuit.

They are controlled by special adaptors (eg. monochrome or graphic adaptors), which are integrated in the central processing unit of the automatic data processing machine. . Their display pitch size starts at 0.41 mm for medium resolution and gets smaller as resolution increases.

Sor to accommodate the presentation of small, yet well-defined images, computer monitors utilise smaller dot (pixel) sizes and greater convergence standards than those applicable to television receivers. In computer monitors, the video frequency (bandwidth), which is the measurement determining how many dots can be transmitted per second to form an image, is generally 15 MHz or greater. But in case of TV or video monitors, the bandwidth is generally not more than 6 MHz.

The horizontal scanning frequency of these monitors varies according to the standards for various display modes, generally from 15 kHz to over 155 kHz. Some are capable of multiple horizontal scanning frequencies. Horizontal scanning frequency of video/TV monitors is fixed, usually 15.6 or 15.7 kHz depending on applicable television standard.

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ANSWER II: In all computer monitors, the image is painted on the screen by an electron beam that scans from one side of the display to the other. In television, transitions in colour, intensity, and pattern as the beam scans across the screen tend to be gradual.

But, the transitions a computer monitor typically processes are abrupt as areas of high intensity transform to areas of black as text is placed on the screen. Television uses a process that relies on the brain’s ability to integrate gradual transitions in pattern that the eye sees as the image is painted on the screen. During the first phase of screen drawing, even-numbered lines are drawn. In the next, odd lines are drawn. The eye integrates the two images to create a single image. The scan is interlaced. But, a computer viewer has different needs. The viewer is sitting within a foot or two of the screen and viewing a frequently changing text image.

If a computer monitor used the same method of display as TV, many transitions would produce an annoying amount of flicker, because the brain is less able to integrate the dramatic transition from bright to dark.

Also, a secondary problem occurs due to inability of the monitor to paint interlaced images exactly in between the lines from preceding scan.

Text images makes this much more visible to the eye at the close range, and at the relatively slower speeds of an interlaced scan. So, computer monitors use a technique that paints one continuous image at a time and is said to be non-interlaced.

Consequently, although the scan frequencies of the TV receiver and monitor are similar, computer monitors must be designed to paint every line during every write of the picture to prevent flicker. This requires electronics that operate twice the speed as that of a television. Courtesy : The Hindu

What is the pH of rainwater? Is the pH suitable for drinking?

The technical definition of pH is that it is a measure of the activity of the hydrogen ion (H+). It is essentially a measure of acidity. The pH scale ranges from 0 -14. In the scale the reading ‘7’ denotes the neutral point. A substance can be rated acidic or basic depending on its pH value. It will be rated as acidic if it has a pH of less than 7 and basic if it is greater.

Normal rainwater has a pH of 5.6 (slightly acidic). This is because it is exposed to the carbon dioxide in the atmosphere. The carbon dioxide gets dissolved in the rainwater and forms carbonic acid (H{-2}CO{-3}).

Rainwater with ph value below 5.6 is considered as acid rain. There are both natural and non-natural sources of materials that cause pH of rain water to change.

Increasing pollution results in acid rains. The primary air pollutants are sulphur dioxide and nitrogen oxide. These pollutants are released into the air due to many factors and burning fossil fuels (ex: coal) is one of the major causes.

Generally rainwater is pure and potable. The pH of drinking water falls in the range of 6.5- 8.

Therefore if the pH of rainwater centres around this value it is fit for drinking. Also the pH of rainwater differs from place to place. This is due to heavy pollution in one area and clean air in another.

In the present scenario urbanization has increased its acidity. But in case of rains whose pH generally falls around 5.6, it is potable, but it will be slightly acidic and corrosive.

But in and around cities and other industrially developed areas where the pH of rainwater tends to fall drastically, rainfall is highly acidic and the water thereby becomes unfit for consumption. Courtesy : The Hindu

In the past, why was injection administered in the stomach for dog bite?

ANSWER I: This is the only disease where the vaccine is given after the exposure (post-exposure). Nervous tissue vaccine (NTV), is one of the vaccines administered for dog bite.

This vaccine is prepared from a fixed virus grown in the brain of adult sheep or other animal. The final vaccine is a 5 per cent emulsion of infected sheep’s brain containing the inactivated virus.

These viruses do not cause the disease but still retain the antigenecity, i.e., capability of producing the antibodies when injected.

After the bite, about 2-5 ml of the vaccine is administered depending upon the bite severity. More vaccine is administered for a longer duration for severe bites. Bites in the neck, head, face, palm, fingers and multiple wounds are categorised as class three bites.

They require injection for 10 days daily with two booster doses. For such volume of vaccine and duration, the ideal injection site is the anterior abdominal wall. This is preferred as there is a wide area and injection can be given at different points to avoid pain, swelling and discomfort.

Moreover the injections are to be given subcutaneously (below the skin) in the fatty layer. It is a misconception that it is given in the stomach. The needle does enter the abdominal cavity or, for that matter, any of the abdominal organs.

On the abdominal wall skin is held in a fold and elevated. A 1.5 cm needle is used to inject the vaccine in the subcutaneous tissue. After the fold is elevated and such a needle is used there is no possibility of going beyond the subcutaneous layer of the anterior abdominal wall.

This anterior abdominal wall is divided into ten quadrants and injections are given in different quadrants each time. This again results in less pain and swelling.

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ANSWER II: The vaccine is given in the stomach region because of the presence of large subcutaneous layer there. Earlier version of this injection needs slower absorption and prolonged activity. Only injection given to a subcutaneous layer can achieve this.

Buttocks and arm region contain larger area of muscle and less of subcutaneous layer.

Hence they are not suitable sites. One more reason is that the stomach region can also accommodate large doses and avoid any complication.

In children despite the subcutaneous layer not being thick and stomach not being large pose no problem as the quantity of injection given is less.

The improved version is a cell cultured vaccine and acts the same way as any other vaccine. In other words it does not require a subcutaneous layer. Hence, it can be given in the buttocks or arm region Courtesy : The Hindu

How does scratching cure itching sensation?

Very sensitive, rapidly adapting, mechanoreceptive free nerve endings that elicit only the tickle and itch sensation are found almost exclusively in the superficial layers of the skin. This sensation is transmitted by very small type – C nerve fibres. These nerve fibres are unmyelinated fibers with a diameter of 0.5 to 2 microns. These fibres transmit impulses as slowly as 0.5 m/sec, unlike the type – A fibres, which transmit impulses at velocities as great as 120 m/sec.

The process of scratching can relieve itch. This scratch reflex is the important spinal cord reflex found in some animals including man. This reflex is initiated by the itch and tickle sensation. It involves two different functions (1) a position sense that allows the hand to find the exact point of irritation on the surface of the body and (2) a to and fro scratching movement. This scratching removes the irritant and the itch is relieved. Sometimes the scratch is strong enough to elicit pain. The pain signals are believed to suppress the itch signals in the cord by the process of lateral inhibition. This lateral inhibition is by the transmission of sensory signals by the anterolateral system, in contrast to the dorsal column system. The anterolateral system is a cruder type of transmission system than the dorsal column system. Courtesy : The Hindu

Why does sea water not erode coastal areas in all places?

The main cause of coastal erosion is the kinetic energy of wind. The main medium of transmission of wind energy is through wind generated water waves.

Occasionally waves are also generated by other forms of energies such as earthquakes (sometimes at sea beds). The waves in turn cause erosion upon breaking on the shoreline or by way of wave induced currents. In coasts where substantial tidal variation occurs (as in Mumbai) there may be marginal erosion.

While erosion of loose materials like sand is visible clearly, it is not so with hard materials like rock. It may be interesting to note, that where the water is still and calm, as in a lagoon, the coastline is be stable. Also to be noted, is the phenomenon of beach formation due to littoral drift ( as in Chennai Marina), stopped by the harbour structures jutting into the sea. Courtesy : The Hindu

Do animals also have blood groups like humans?

In man blood group is applied to single factor. This factor is agglutinogen and is also called antigen. It is found on the surface of red blood corpuscles.

Accordingly a person with ‘A’ antigen is designated as a person with A-group, with ‘B’ antigen as B-group, with both A and B antigens as AB-blood group and a person without any antigens is designated as O-blood group.

In the case of animals blood group is applied to combinations of blood factors. So it is preferable to call it as blood group systems rather then blood groups. Each system has many factors, which are together called blood group factors.

Dr. J. Moustgaard, of the Royal Veterinary & Agricultural College, Copenhagen has identified in cattle ten group systems namely A,B,C,FV,J,L,M,SU, Z and R’S’. Except J and L, all the other group systems have more than one group factor. For example the group factors of the group system A are designated as A{-1}, A{-2}, D, H, Z’.

The grouping factors are particular serum proteins. Acquiring of each protein is an inherited character. So examination of blood sample from within a breed might eventually prove a very useful means of selection. It might also indicate what mating could be expected to result in infertility.

The B-group system only has greater number of grouping factors. It has nearly 27 group factors, which are called phenogroups. Some of these are unique to particular breeds.

They are particularly valuable in determining incorrectly stated parentage. In dogs serum major groups have been recognised in the USA and they are referred to as A to G.

In veterinary practice blood transfusion is used in cases of haemorrhage and shock and to a lesser extent as part of the treatment of certain infectious diseases.

In cattle the donor and recipient are usually in the same herd. This fact lessens the risk of introducing infection and incompatibility does not arise.

But normal antibodies against the blood group factor-J are sometimes found in cattle. Thus if the donor’s blood is J-positive and the recipient’s blood contains normal antibody called anti-J the so-called transfusion reaction might be expected immediately following blood transfusion. These reactions are dyspnoea, muscular twisting, increased salivation and circulatory disturbances.

However, if an animal has been exposed to repeated blood transfusions, a different situation will arise. The animal will now have formed antibodies against the blood group antigens it does not have itself. It is therefore by no means unlikely that the blood of donor and the recipient are incompatible.

If this is so, transfusion will set off strong transfusion reactions. Such reaction can occur on the second or on subsequent blood transfusion. Courtesy : The Hindu

What is Computer Simulation Technique?

ANSWER I: ‘Simulation’ in general terms can be defined as the representation or imitation of a system in its realistic form. When a computer program is used to create a model to mimic a real world system, then the term ‘computer simulation’ comes into action. Such models are called computer simulated models. Computer simulation is of two types. One is called discrete simulation, in which, a system is observed only at some fixed regular time points, an example of which is the queuing system. It is a system where the events or jobs arrive at a time and wait in the queue to be processed. Generally the queue operates in a FIFO (First In First Out) fashion. Some real time examples for this case can be customers waiting in the queue in banks or to buy groceries in departmental stores. The involvement of the computer here is to maintain the queue according to the arrival time of the event, in this case the customers, and process each event one after the other according to their arrival time.

The other type is called Analogue simulation, which involves traditional mathematics. This is applied to a system whose state varies continuously in time. In this technique, sets of differential equations were used to describe a system. Since computers have the ability to solve equations, using various algorithms, in minimal time, its usage was very much relevant here. Some examples of this type are cosmology systems and chemical applications, which involve a large number of equations and require huge computing power.

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ANSWER II: To simulate a phenomenon, on a computer, we need a mathematical model that imitates the phenomenon. As an example consider the motion of Earth around the sun. The sun and Earth attract each other.

Once we model this gravitational force we can simulate the elliptic orbit of Earth. Here we do not need a computer since the governing equation is simple.

But consider a projectile hurled in the atmosphere. Here the friction of air plays an important role. The trajectory can be stimulated by approximate numerical techniques. We start with the condition of the projectile (position and velocity; then frictional force is known) at some instant. We can calculate its condition after a very small interval.

Then the new value for friction can be evaluated. We continue this process of numerical integration to get the trajectory. Smaller the time interval employed more accurate is the solution. This is where the computer enters to make the job easy. Complex fluid flow phenomena like turbulent flows, vibration of an aeroplane frame, combustion, weather and ocean circulation are some of the examples that need huge computer power. Courtesy : The Hindu

How does ballast-less track provide safe travel?

ANSWER I: Ballast is a prime component of the track that acts as a vibrant medium to transmit from the rail surface the weight of the train down to the formation, the wells set on prepared terrain. It ensures a cushioned and smooth run for the train and precludes the longitudinal displacement of the rail called creep. In ballast-less track, as the name suggests the ballast is replaced by a bed of concrete. The rails rest on rubber pads placed over concrete sleepers, which are fixed on the concrete bed.

The ballast-less track helps to eliminate the evils of dust and noise pollution and proves suitable for underground railway also. So it is also safe for travel.

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ANSWER II: The MRTS in Chennai is equipped with a ballast-less track. The rubber pads on which the rails rest help to absorb the vibration caused due to the movement of the train. The cost involved in laying a ballast-less track is more initially but it requires less recurring maintenance cost. Courtesy : The Hindu

How do certain species of birds such as Humming Birds, Terns, Gulls and Kestrels remain in the air without a forward motion?

ANSWER I: The humming bird’s wings consist mainly of elongated hand bones to which the flight feathers are attached, and the whole wing can rotate as does the wrist.

The short arm bones not only allow movement in all directions but can also accommodate axial rotation through 180 degrees. The tips of the wings are capable of achieving a great deal of controlled movements. Birds have two sets of muscles operating the wings.

One powers the down-strokes and the other provides the upstroke or lifts the wings. A humming bird has more number of muscles to lift it upwards.

The angles through which the wings can be twisted and rotated by means of the big muscles that give the upstroke, can convert even the upstroke into a power movement providing both lift and propulsion.

Thus the bird is able to hover in perfectly still air, its quivering wings moving rapidly backwards and forwards rather than up and down, the tips of the primary feathers tracing a figure of eight.

Every time the beat is reversed, the wings are pivoted through 180 degrees, this ensuring that the front edge always leads, and on the back stroke, it is always the underside of the flight feathers which are on the top.

This means that although forward and backstrokes both produce lift the two actually cancel each other out and leave the bird still on station with no movement.

The kestrel and kingfisher are adept at this, but it does not constitute true hovering. Humming birds are able to maintain their hovering in perfectly still air, a feat totally beyond the kestrel which, true to its vernacular name of wind hover, cannot function unless a breeze is flowing, even though this can be so slight that at ground it may not be noticeable to a human observer. Reference: How Birds work. A guide to bird biology.

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ANSWER II: Wings of hummingbirds are adapted to a helicopter-like flight. They can move their wings from shoulder and can beat them up to 70 beats per second. They have two sets of flight muscles.

They are the pectoralis majors (one left and one right), which are attached to the sternum and keel, the upper wing bones (humerus), and the clavicles (which are fused at the tip to form the furcula, or wishbone). The pectoral muscles pull the wings down, which causes forward motion of the bird.

The wings are raised by the supracoracoideus muscles (right and left), which in hummingbirds are particularly large — about half the size of the pectorals.

Hummingbirds can rotate their wings backward, which creates downward ‘lift’ and backward ‘thrust’. By alternating their wings forward and backward, the up and down forces and forward and back forces cancel each other out, enabling the bird to hover in one place.

, . They are the only birds which can fly forwards, backwards, up, down, sideways or move instantaneously in any direction Courtesy : The Hindu

How is carbon dioxide removed from blood before it is exhaled?

In humans, carbon dioxide is generated in the tissues during oxidation of glucose, in order to liberate energy, which is resumed to perform body functions. Before exhalation through lungs the gas is transported from the tissues to the lungs. Under normal resting conditions an average of 4 millilitres of CO{-2} is transported from the tissues to the lungs in each decilitre of blood.

This transport is performed by venous system of the body and pulmonary artery of the heart. The venous system first transports deoxygenated blood carrying CO{-2} to the heart. From there, blood is transported to lungs for purification by the pulmonary artery.

To begin with CO{-2} diffuses out of the tissue cells in the dissolved molecular CO{-2} form. On entering the capillary, it initiates a host of almost instantaneous physical and chemical reactions. A small portion of the CO{-2} is transported in a dissolved state to the lungs. This is about 7 per cent of all the CO{-2} transported.

Nearly 70 per cent of CO{-2} is transported as bicarbonate ions. The dissolved CO{-2} in the blood first reacts with water to form carbonic acid. This can be effected by the enzyme carbonic anhydrase, which catalyse the reaction between CO{-2} and water, accelerating 5000-fold.

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Since the enzyme is found only in the red blood cells (RBC) carbonic acid formation is so rapid in them than in the plasma. In the red blood cells it occurs in a small fraction of a second. In no time the carbonic acid formed in the red blood cells dissociates into hydrogen ions (H{++}) and bicarbonate ions (HCO{-3}) ions. Most of the H{++} ions then combine with the haemoglobin (Hb) in the red blood cells because Hb is a powerful acid-base buffer. In turn, many of the bicarbonate ions diffuse into the plasma while chloride ions diffuse into the red cells to take their place.

This is possible by the presence of a special bicarbonate carrier protein in the red cell membrane that shuttles the two ions in opposite directions at rapid velocities. Thus, the chloride content of venous red blood cells is greater than that of arterial cells, a phenomenon called the chloride shift. In the alveolar capillaries the carbonate ions under the influence of carbonic anhydrase by reversible reaction again produce the CO{-2} and water molecules. These CO{-2} molecules are then easily released into the alveoli for exhalation.

Transport of CO{-2} in combination with haemoglobin is also possible. In addition to reacting with water, CO{-2} also reacts directly with haemoglobin to form the compound of carbaminohaemoglobin (CO{-2}HHb).

This combination of carbon dioxide with the haemoglobin is a reversible reaction that occurs with a very loose bond, so that the carbon dioxide is easily released into the alveoli where the partial pressure of CO{-2} is lower than the tissue capillaries. Nearly 23 per cent of CO{-2} is transported this way. Courtesy : The Hindu

Why is the Earth’s core hot? What caused it to heat up? Is it still heating, or now cooling?

Scientists estimate that temperature at the Earth’s core is about 5538{+0}C.

Much of the heat inside the Earth today comes from elements that were present when the planet was first formed billions of years ago. One theory is that radioactive decay of the primordial elements inside the Earth, U-238, Th-232, and U-235 and their radioactive products generate thermal energy (heat).

A nucleus — the central core of an atom — contains both protons and neutrons. Elements, such as the ones mentioned above, have a fixed number of protons but may exist with various numbers of neutrons.

The sum of the protons and neutrons makes up the mass number of an element. Isotopes of an element have the same chemical properties but different weights (indicated by the mass number). Radioactive elements are isotopes with an unstable nucleus.

The isotopes decay by emitting energetic alpha and beta particles until stability is reached. Alpha particles are the nuclei of ordinary helium atoms, which consist of two protons and two neutrons. Beta particles are electrons or positrons. The half-life of an isotope is the amount of time it takes for half of the atoms to decay into a more stable form.

Within the Earth, the released particles from the elements are slowed by friction through interaction with Earth material, thereby generating heat.

The primordial radioactive elements have half-lives on the order of a billion years. Hence, since the Earth formed, their abundance is decreasing over time as a function of their half-life. Therefore, Earth’s core is not heating up, it’s cooling down. Courtesy : The Hindu

Why does rain come in drops and not in a continuous stream?

When warm wet air rises, it cools and water vapour condenses to form clouds. A cloud is made of small drops of water or ice crystals, depending on its height and how cold its surrounding air is. Most rain originates in nimbus or in towering cumulonimbus clouds.

To form rain, water vapour needs what’s called a condensation nucleus, which can be tiny particles of dust, or pollen, swept up high into the atmosphere. When the condensing droplets that form the cloud get large and heavy enough to overcome the upward pressure of convection, they begin to fall.

Although all clouds contain water, some produce precipitation and others drift away placidly without giving rain. First all the droplets in a cloud are less than 20 micrometer in diameter. In a cloud there are lot hygroscopic particles and normally drops form by absorbing moisture by these particles.

Rain is restricted to drops of water that fall from a cloud. They have a typically diameter of at least 0.5 mm. A raindrop large enough to reach the ground without evaporating contains roughly a million times the water of a cloud droplet (typical diameter is 0.012 mm). No matter what the intensity of rain is the size of the drop rarely exceeds about 5 mm. Larger drops do not survive as the process of surface tension which holds the drop together is exceeded by the frictional drag of air and therefore larger drops break apart into smaller ones.

Raindrops as they descend, initiate a chain reaction, a downward trend of the water droplets, with the larger drops always breaking — a common feature observed when one forcefully disgorge the contents of a glass of water.

Most rainfall begins as snow crystals or other solid forms. Entering the warmer air below the cloud, these ice particles often melt and reach the ground as raindrops.

A raindrop starts falling and then picks up speed due to gravity. When one drop starts falling a wake follows in the cloud. (Wake is a clearance that is normally found behind a speeding boat.) This clearance is convenient for another drop to follow and not exactly in the same path but close to it, says Mr. C. Ranganathan of Tiruchy.

Drops that pick up speed are slowed down by the drag of the surrounding air. Indeed the smallest drop may not fall at all, being suspended or perhaps forced upward by ascending currents of air until they grow large enough to fall. As larger droplets descent, they produce an airstream around them.

The larger the cloud droplet the better the chance of its colliding with a giant droplet. So each drop falls at a different speed as their sizes are different. There are collisions between raindrops. Some collisions cause drops to coalesce, forming a large drop and some cause drops to break into smaller ones. As the number of drops grows the intensity of rain increases.

Collision does not guarantee coalescence. Experiments have indicated that the presence of atmospheric electricity may be the key to what keeps the drops together as they collide. That is when a droplet with a negative charge collides with another with a positive charge their electrical attraction may hold them together.

Rate at which drops fall is size dependent. Giant droplets fall rapidly. Thus drops keep on falling side by side and not in a continuous stream. Courtesy : The Hindu

As early as 1852, it was discovered by researchers that synthetic small needle-shaped crystals of iodosulphate of quinine possess the property of polarising light. These crystals are not stable. A Polaroid sheet is prepared from the suspension of these crystals of nitrocellulose. To impart stability, its thin sheet is mounted between two sheets of glass or celluloid.

It can also be obtained by stretching a thin sheet of polyvinyl alcohol strained with iodine. When such a sheet is subjected to a large strain, the molecules get oriented in the direction of applied strain. If the stretched sheet of polyvinyl alcohol is heated in the presence of a dehydrating agent such as hydrochloric acid, it becomes strongly stable. Each polaroid sheet is enclosed between thin glass plates so as to provide mechanical support.

Polaroids are of two types. H-polaroid and the k-polaroid. The main difference is that k-polaroid are not strained with iodine.

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ANSWER II: A light wave vibrating in more than one plane is referred to as unpolarised light. Polarised light waves are those in which the vibrations occur in a single plane. It is possible to transform unpolarised light into a polarised one and this process is called polarisation.

A Polaroid filter is able to polarize light because of the chemical composition of the filter material. The molecules of the filters are all oriented along the same direction so that they all absorb light of the same polarisation.

When light reflects from a horizontal surface at an angle, the reflected light tends to be polarised horizontally. At a specific angle, the light is completely horizontally polarised because any vertically polarised light that hits the surface at this angle is allowed to enter the surface without reflection. Since reflections from horizontal surfaces are mostly horizontally polarised, glare is mostly horizontally polarised.

Polarising sunglasses deliberately block horizontally polarised light to reduce glare. There are several types of lens material. CR-39 is a plastic made from hard resin that meets optical quality standards. Polycarbonate is a synthetic plastic material that has great strength and is very lightweight.

Eyeglasses that darken when exposed to the sun are called photochromatic. Photochromatic lenses rely on a specific chemical reaction to UV radiation.

These lenses have millions of molecules of substances, such as silver chloride or silver halide, embedded in them. The molecules are transparent to visible light in the absence of UV light. But when exposed to UV rays in sunlight, the molecules undergo a chemical process that causes them to change shape. The new molecular structure absorbs portions of the visible light, causing the lenses to darken. The number of the molecules that change shape varies with the intensity of the UV rays.

When we go indoors and out of the UV light, the reverse chemical reaction takes place. The sudden absence of UV radiation causes the molecules to return to their original shape, resulting in the loss of their light absorbing properties. Courtesy : The Hindu

Why is the @ symbol used in an email address?

ANSWER I: The e-mail address generally has two parts, user id and the domain name. The @ (at) symbol is used to separate the user id from the domain name in the e-mail address.

These addresses can be compared to the addresses of the houses in a huge colony. Examples are Hotmail, Yahoo, Sify and AOL.The domains are in turn classified as sub-domains for the sake of clarity in large organisations. Some of the top-level domains (TLD’s) are

com, .edu, .net,.gov.

The ‘@’ symbol indicates that the user can be reached on the Internet by giving the email address(also called the User’s Uniform Resource Locator (URL)). Courtesy : The Hindu

How does the solar wind affect Earth?

Solar wind contains intense clouds of high energy particles which are produced by solar storms. These clouds of particles affect Earth. These clouds are called coronal mass ejections. They reach the earth in three to four days. The coronal mass ejections cause changes in the magnetic field of the earth when they collide with the field.

They cause more changes to the magnetic field at times even at lower altitudes close to the ground when they leak through the field especially near the north and south poles. These changes can produce many problems with electrical equipment.

Not much light has been thrown on the way in which solar wind ‘plasma’ invades the Earth’s magnetic field and seeps into the inner regions where the van Allen radiation belts are located.

Also, in the direction opposite the Sun, the Earth’s magnetic field is pulled way out into interplanetary space making it look like a comet. Many different electrical disturbances take place in this ‘geotail’ region.

These can accelerate particles to high speeds and energies. All of this is made much more violent by the solar wind, especially the storm clouds that the Sun launches our way very often Courtesy : The Hindu

How do touch screens work?

Touch screen monitors — where you can use your finger on the computer screen to navigate through the contents — have become more and more commonplace over the past decade, particularly at public information kiosks. A basic touch screen has three main components: a touch sensor, a controller, and a software driver. The touch screen is an input device, so it needs to be combined with a display and a PC to make a complete touch input system.

The Touch Sensor has a textured coating across the glass face. This coating is sensitive to pressure and registers the location of the user’s finger when it touches the screen. The controller is a small PC card that connects the touch sensor to the PC. It takes information from the touch sensor and translates it into information that PC can understand. The Software Driver is a software update for the PC system that allows the touchscreen and computer to work together. It tells the computer’s operating system how to interpret the touch event information that is sent from the controller.

There are three basic systems that are used to recognise a person’s touch — Resistive, Capacitive and Surface acoustic wave.

The resistive system consists of a normal glass panel that is covered with a conductive and a resistive metallic layer. These layers are held apart by spacers, and a scratch-resistant layer is placed on top of the whole set up. An electrical current runs through the two layers while the monitor is operational. When a user touches the screen, the two layers make contact in that spot. The change in electrical field is noted and coordinates of the point of contact are calculated. Once the coordinates are known, a special driver translates the touch into something that the operating system can understand, much as a computer mouse driver translates a mouse’s movements into a click or drag.

In the capacitive system, a layer that stores electrical charge is placed on the glass panel of the monitor. When a user touches the monitor with his or her finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch screen driver software. One advantage of the capacitive system is that it transmits almost 90 per cent of the light from the monitor, whereas the resistive system only transmits about 75 per cent. This gives the capacitive system a much clearer picture than the resistive system.

The surface acoustic wave system uses two transducers (one receiving and one sending) placed along the x and y axes of the monitor’s glass plate. Also placed on the glass are reflectors — they reflect an electrical signal sent from one transducer to the other. The receiving transducer is able to tell if the wave has been disturbed by a touch event at any instant, and can locate it accordingly. The wave setup has no metallic layers on the screen, allowing for 100-percent light throughput and perfect image clarity. This makes the surface acoustic wave system best for displaying detailed graphics (both other systems have significant degradation in clarity).

Another area in which the systems differ is which stimuli will register as a touch event. A resistive system registers a touch as long as the two layers make contact, which means that it doesn’t matter if you touch it with your finger or a rubber ball. A capacitive system, on the other hand, must have a conductive input, usually your finger, in order to register a touch. The surface acoustic wave system works much like the resistive system, allowing a touch with almost any object — except hard and small objects like a pen tip. (Source: www.howstuffworks.com and www.touchscreens.com ) Courtesy : The Hindu

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